Dropdown menus can also be toggled from the bottom up by adding a single class to the immediate parent of .dropdown-menu. It will flip the direction of the caret and reposition the menu itself to move from the bottom up instead of top down.
<div class="btn-group dropup">
<button class="btn btn-info dropdown-toggle" data-toggle="dropdown">Action <i class="fa fa-caret-up"></i></button>
<ul class="dropdown-menu" role="menu">
<li><a href="#" tabindex="-1">Action</a></li>
<li><a href="#" tabindex="-1">Action Two</a></li>
</ul>
</div>