<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script> <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <!------ Include the above in your HEAD tag ----------> <div class="panel-group" id="accordion1"> <div class="panel panel-default"> <div class="panel-heading"> <h4 class="panel-title"> <a data-toggle="collapse" data-parent="#accordion1" href="#collapseThree">Collapsible Group Item #3 </a> </h4> </div> <div id="collapseThree" class="panel-collapse collapse"> <div class="panel-body"> <div class="panel-group" id="accordion2"> <div class="panel panel-default"> <div class="panel-heading"> <h4 class="panel-title"> <a data-toggle="collapse" data-parent="#accordion2" href="#collapseThreeOne">Collapsible Group Item #3.1 </a> </h4> </div> <div id="collapseThreeOne" class="panel-collapse collapse"> <div class="panel-body">Panel 3.1</div> </div> </div> <div class="panel panel-default"> <div class="panel-heading"> <h4 class="panel-title"> <a data-toggle="collapse" data-parent="#accordion2" href="#collapseThreeTwo">Collapsible Group Item #3.2 </a> </h4> </div> <div id="collapseThreeTwo" class="panel-collapse collapse"> <div class="panel-body">Panel 3.2</div> </div> </div> </div> </div> </div> </div> </div>