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-primary">Dropup</button>
<button class="btn btn-primary dropdown-toggle" data-toggle="dropdown"><i class="icon-caret-up "></i></button>
<ul class="dropdown-menu">
<li><a href="#">Action</a></li>
<li><a href="#">Another action</a></li>
<li><a href="#">Something else here</a></li>
<li class="divider"></li>
<li><a href="#">Separated link</a></li>
</ul>
</div>