<button type="button" class="btn btn-warning" data-toggle="collapse" data-target="#demo-collapse">Show list</button>
  <div id="demo-collapse" class="collapse">
    <ul>
      <li><a href="#">Item 1</a></li>
      <li><a href="#">Item 2</a></li>
      <li><a href="#">Item 3</a></li>
    </ul>
  </div>