I modified the side menu to include a second level menu. but when i open the 1st level, it opens all next levels inside the opened level. it was working perfectly in version 2 bootstrap 3. but it is not working in latest release of version 3 "3.0.0-rc.4".
This my modified menu of starter.html
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</li>
</ul>
</li>
</ul>
</li>
<li class="nav-item">
<a href="pages/widgets.html" class="nav-link">
<i class="nav-icon fas fa-th"></i>
<p>
Widgets
<span class="right badge badge-danger">New</span>
</p>
</a>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-copy"></i>
<p>
Layout Options
<i class="fas fa-angle-left right"></i>
<span class="badge badge-info right">6</span>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/layout/top-nav.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Top Navigation</p>
</a>
</li>
<li class="nav-item">
<a href="pages/layout/boxed.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Boxed</p>
</a>
</li>
<li class="nav-item">
<a href="pages/layout/fixed-sidebar.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Fixed Sidebar</p>
</a>
</li>
<li class="nav-item">
<a href="pages/layout/fixed-topnav.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Fixed Navbar</p>
</a>
</li>
<li class="nav-item">
<a href="pages/layout/fixed-footer.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Fixed Footer</p>
</a>
</li>
<li class="nav-item">
<a href="pages/layout/collapsed-sidebar.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Collapsed Sidebar</p>
</a>
</li>
</ul>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-chart-pie"></i>
<p>
Charts
<i class="right fas fa-angle-left"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/charts/chartjs.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>ChartJS</p>
</a>
</li>
<li class="nav-item">
<a href="pages/charts/flot.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Flot</p>
</a>
</li>
<li class="nav-item">
<a href="pages/charts/inline.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Inline</p>
</a>
</li>
</ul>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-tree"></i>
<p>
UI Elements
<i class="fas fa-angle-left right"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/UI/general.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>General</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/icons.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Icons</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/buttons.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Buttons</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/sliders.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Sliders</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/modals.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Modals & Alerts</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/navbar.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Navbar & Tabs</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/timeline.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Timeline</p>
</a>
</li>
<li class="nav-item">
<a href="pages/UI/ribbons.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Ribbons</p>
</a>
</li>
</ul>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-edit"></i>
<p>
Forms
<i class="fas fa-angle-left right"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/forms/general.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>General Elements</p>
</a>
</li>
<li class="nav-item">
<a href="pages/forms/advanced.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Advanced Elements</p>
</a>
</li>
<li class="nav-item">
<a href="pages/forms/editors.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Editors</p>
</a>
</li>
</ul>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-table"></i>
<p>
Tables
<i class="fas fa-angle-left right"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/tables/simple.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Simple Tables</p>
</a>
</li>
<li class="nav-item">
<a href="pages/tables/data.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>DataTables</p>
</a>
</li>
<li class="nav-item">
<a href="pages/tables/jsgrid.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>jsGrid</p>
</a>
</li>
</ul>
</li>
<li class="nav-header">EXAMPLES</li>
<li class="nav-item">
<a href="pages/calendar.html" class="nav-link">
<i class="nav-icon fas fa-calendar-alt"></i>
<p>
Calendar
<span class="badge badge-info right">2</span>
</p>
</a>
</li>
<li class="nav-item">
<a href="pages/gallery.html" class="nav-link">
<i class="nav-icon far fa-image"></i>
<p>
Gallery
</p>
</a>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon far fa-envelope"></i>
<p>
Mailbox
<i class="fas fa-angle-left right"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/mailbox/mailbox.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Inbox</p>
</a>
</li>
<li class="nav-item">
<a href="pages/mailbox/compose.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Compose</p>
</a>
</li>
<li class="nav-item">
<a href="pages/mailbox/read-mail.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Read</p>
</a>
</li>
</ul>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-book"></i>
<p>
Pages
<i class="fas fa-angle-left right"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/examples/invoice.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Invoice</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/profile.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Profile</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/e_commerce.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>E-commerce</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/projects.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Projects</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/project_add.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Project Add</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/project_edit.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Project Edit</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/project_detail.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Project Detail</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/contacts.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Contacts</p>
</a>
</li>
</ul>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon far fa-plus-square"></i>
<p>
Extras
<i class="fas fa-angle-left right"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="pages/examples/login.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Login</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/register.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Register</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/lockscreen.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Lockscreen</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/legacy-user-menu.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Legacy User Menu</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/language-menu.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Language Menu</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/404.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Error 404</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/500.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Error 500</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/pace.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Pace</p>
</a>
</li>
<li class="nav-item">
<a href="pages/examples/blank.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Blank Page</p>
</a>
</li>
<li class="nav-item">
<a href="starter.html" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Starter Page</p>
</a>
</li>
</ul>
</li>
<li class="nav-header">MISCELLANEOUS</li>
<li class="nav-item">
<a href="https://adminlte.io/docs/3.0" class="nav-link">
<i class="nav-icon fas fa-file"></i>
<p>Documentation</p>
</a>
</li>
<li class="nav-header">MULTI LEVEL EXAMPLE</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="fas fa-circle nav-icon"></i>
<p>Level 1</p>
</a>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="nav-icon fas fa-circle"></i>
<p>
Level 1
<i class="right fas fa-angle-left"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="#" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Level 2</p>
</a>
</li>
<li class="nav-item has-treeview">
<a href="#" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>
Level 2
<i class="right fas fa-angle-left"></i>
</p>
</a>
<ul class="nav nav-treeview">
<li class="nav-item">
<a href="#" class="nav-link">
<i class="far fa-dot-circle nav-icon"></i>
<p>Level 3</p>
</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="far fa-dot-circle nav-icon"></i>
<p>Level 3</p>
</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="far fa-dot-circle nav-icon"></i>
<p>Level 3</p>
</a>
</li>
</ul>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="far fa-circle nav-icon"></i>
<p>Level 2</p>
</a>
</li>
</ul>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="fas fa-circle nav-icon"></i>
<p>Level 1</p>
</a>
</li>
<li class="nav-header">LABELS</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="nav-icon far fa-circle text-danger"></i>
<p class="text">Important</p>
</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="nav-icon far fa-circle text-warning"></i>
<p>Warning</p>
</a>
</li>
<li class="nav-item">
<a href="#" class="nav-link">
<i class="nav-icon far fa-circle text-info"></i>
<p>Informational</p>
</a>
</li>
</ul>
</nav>`
I noticed that style="display: block; is added to all sub trees when parent tree is opened.
I noticed the new sample of multilevel menu has the same issue. level 2 is opened when i open level 1

This behavior started from 3.0.0-rc.2. It was working well till 3.0.0-rc.1
I've fixed this bug in v3-dev branch, coming with the next release rc.5.
AdminLTE v3.0.0-rc.5 is released with this fix.
Most helpful comment
I've fixed this bug in v3-dev branch, coming with the next release rc.5.