问如何允许多选择此引导下拉代码？

EN

<div class="dropdown pull-left dropdown-custom-quicklook">
      <button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown"><i class="icon-filter"></i> Filter By Quick Look</button>
      <ul class="dropdown-menu pull-right keep-open-on-click" role="menu">
         <?php
              foreach($quicklook as $look){
                 echo '<li><a href="">'.$look.'</a></li>';
              }
         ?>
     </ul>
    </div>