lass="text-info">Note:</strong> Bootstrap 4 normally uses <code>&lt;div></code> elements as <code>.dropdown-menu</code> containers. But since we are building a multi-level menu tree, we need to replace them with nested <code>&lt;ul></code>/<code>&lt;li></code> elements.</p>
      <pre class="border rounded p-3 bg-light">&lt;!-- Navbar -->
&lt;nav class="navbar navbar-expand-lg navbar-dark bg-dark mb-4">
  &lt;div class="container">
    &lt;a class="navbar-brand" href="#">Navbar&lt;/a>
    &lt;button class="