<nav id="navbar-example3" class="navbar navbar-light bg-light flex-column align-items-stretch p-3">

  <a class="navbar-brand" href="#">Navbar</a>

  <nav class="nav nav-pills flex-column">

    <a class="nav-link" href="#item-1">Item 1</a>

    <nav class="nav nav-pills flex-column">

      <a class="nav-link ms-3 my-1" href="#item-1-1">Item 1-1</a>

      <a class="nav-link ms-3 my-1" href="#item-1-2">Item 1-2</a>

    </nav>

    <a class="nav-link" href="#item-2">Item 2</a>

    <a class="nav-link" href="#item-3">Item 3</a>

    <nav class="nav nav-pills flex-column">

      <a class="nav-link ms-3 my-1" href="#item-3-1">Item 3-1</a>

      <a class="nav-link ms-3 my-1" href="#item-3-2">Item 3-2</a>

    </nav>

  </nav>

</nav>

​

<div data-bs-spy="scroll" data-bs-target="#navbar-example3" data-bs-offset="0" tabindex="0">

  <h4 id="item-1">Item 1</h4>

  <p>...</p>

  <h5 id="item-1-1">Item 1-1</h5>

  <p>...</p>

  <h5 id="item-1-2">Item 1-2</h5>

  <p>...</p>

  <h4 id="item-2">Item 2</h4>

  <p>...</p>

  <h4 id="item-3">Item 3</h4>

  <p>...</p>

  <h5 id="item-3-1">Item 3-1</h5>

  <p>...</p>

  <h5 id="item-3-2">Item 3-2</h5>

  <p>...</p>

</div>