jQuery/Bootstrap : dropdown-toggle is not setting the selected menu item as default selected item

I have a bootstrap dropdown but i am not able to set the selected menu item as default selected dropdown item?

<div class="dropdown">
   <button class="btn dropdown-toggle" type="button" id="drpDownCat" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true"> Select a Category<span class="caret"></span>
   </button>
   </button>

    <ul class="dropdown-menu" aria-labelledby="drpDownCat">
       <li><a class="dropdown-item" href="#">Category 1</a></li>
       <li><a class="dropdown-item" href="#">Category 2</a></li>
       <li><a class="dropdown-item" href="#">Category 3</a></li>
       <li><a class="dropdown-item" href="#">Category 4</a></li>
   </ul>
</div>

   <script>
   $('.dropdown-toggle').click(function()
     {
       $('.dropdown-men').toggle();
     }

   </script>