Bootstrap嵌套

<div class = "btn-group">
   <button type = "button" class = "btn btn-default">Button 1</button>
   <button type = "button" class = "btn btn-default">Button 2</button>

   <div class = "btn-group">
      <button type = "button" class = "btn btn-default dropdown-toggle" data-toggle = "dropdown">
         Dropdown
         <span class = "caret"></span>
      </button>

      <ul class = "dropdown-menu">
         <li><a href = "#">Dropdown link 1</a></li>
         <li><a href = "#">Dropdown link 2</a></li>
      </ul>
   </div>

</div>