<div class="container">
  <div class="panel-group" id="accordionMenu" role="tablist" aria-multiselectable="true">
    <div class="panel panel-default">
      <div class="panel-heading" role="tab" id="headingOne">
        <h4 class="panel-title">
        <a role="button" data-toggle="collapse" data-parent="#accordionMenu" href="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
          Menu 0
        </a>
      </h4>
      </div>
      <div id="collapseOne" class="panel-collapse collapse in" role="tabpanel" aria-labelledby="headingOne">
        <div class="panel-body">
          <ul class="nav">
            <li><a href="#">item 1</a></li>
            <li><a href="#">item 2</a></li>
            <li><a href="#">item 3</a></li>
          </ul>
        </div>
      </div>
    </div>
    <div class="panel panel-default">
      <div class="panel-heading" role="tab" id="headingTwo">
        <h4 class="panel-title">
        <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordionMenu" href="#collapseTwo" aria-expanded="false" aria-controls="collapseTwo">
          Menu 1
        </a>
      </h4>
      </div>
      <div id="collapseTwo" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingTwo">
        <div class="panel-body">
          <ul class="nav">
            <li><a href="#">item 1</a></li>
            <li><a href="#">item 2</a></li>
            <li><a href="#">item 3</a></li>
            <li><a href="#">item 4</a></li>
          </ul>
        </div>
      </div>
    </div>
    <div class="panel panel-default">
      <div class="panel-heading" role="tab" id="headingThree">
        <h4 class="panel-title">
        <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordionMenu" href="#collapseThree" aria-expanded="false" aria-controls="collapseThree">
          Menu 2
        </a>
      </h4>
      </div>
      <div id="collapseThree" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingThree">
        <div class="panel-body">
          <ul class="nav">
            <li><a href="#">item 1</a></li>
            <li><a href="#">item 2</a></li>
            <li><a href="#">item 3</a></li>
            <li><a href="#">item 4</a></li>
          </ul>
        </div>
      </div>
    </div>
    
    
    <div class="panel panel-default">
      <div class="panel-heading" role="tab" id="headingFour">
        <h4 class="panel-title">
        <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordionMenu" href="#collapseFour" aria-expanded="false" aria-controls="collapseFour">
          Menu 3
        </a>
      </h4>
      </div>
      <div id="collapseFour" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingFour">
        <div class="panel-body">
          <ul class="nav">
            <li><a href="#">item 1</a></li>
            <li><a href="#">item 2</a></li>
          </ul>
        </div>
      </div>
    </div>
    
  </div>
</div>

body {
  color: #6a6c6f;
  background-color: #f1f3f6;
  margin-top:30px;
}

.container {
  max-width: 960px;
}

ul {
  margin: 0;
  padding: 0;
  list-style: none;
}

.nav li {
  border-bottom: 1px solid #eee;
}

.nav li a {
  font-size: 14px;
}

#accordionMenu {
  max-width: 300px;
}

.panel-body {
  padding: 0;
}

.panel-group .panel+.panel {
  margin-top: 0;
  border-top: 0;
}

.panel-group .panel {
  border-radius: 0;
}

.panel-default>.panel-heading {
  color: #333;
  background-color: #fff;
  border-color: #e4e5e7;
  padding: 0;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}

.panel-default>.panel-heading a {
  display: block;
  padding: 10px 15px;
  text-decoration: none;
}

.panel-default>.panel-heading a:after {
  content: "";
  position: relative;
  top: 1px;
  display: inline-block;
  font-family: 'Glyphicons Halflings';
  font-style: normal;
  font-weight: 400;
  line-height: 1;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  float: right;
  transition: transform .25s linear;
  -webkit-transition: -webkit-transform .25s linear;
}

.panel-default>.panel-heading a[aria-expanded="true"] {
  background-color: #eee;
}

.panel-default>.panel-heading a[aria-expanded="true"]:after {
  content: "\e113";
}

.panel-default>.panel-heading a[aria-expanded="false"]:after {
  content: "\e114";
}