<ul id="net">
  <li><span class="net1">Menu</span>
    <ul class="net2">
      <li>Pages#1</li>
      <li>Pages#2</li>
      <li><span class="net1">Menu#1</span>
        <ul class="net2">
          <li>Pages#1</li>
          <li>Pages#2</li>
          <li><span class="net1">Menu#2</span>
            <ul class="net2">
              <li>Pages#1</li>
              <li>Pages#2</li>
              <li>Pages#3</li>
              <li>Pages#4</li>
            </ul>
          </li>
        </ul>
      </li>  
    </ul>
  </li>
</ul> 

body{
font-family: Tahoma;
font-size: 20px;
text-transform: capitalize;
color:#fff;
}
ul, #net {
  list-style-type: none;
}

#net {
  margin: 0;
  padding: 0;
}

.net1 {
  cursor: pointer;
  -webkit-user-select: none; /* Safari 3.1+ */
  -moz-user-select: none; /* Firefox 2+ */
  -ms-user-select: none; /* IE 10+ */
  user-select: none;
}

.net1::before {
  content: "\25B6";
  color: red;
  display: inline-block;
  margin-right: 6px;
}

.net1-down::before {
  -ms-transform: rotate(90deg); /* IE 9 */
  -webkit-transform: rotate(90deg); /* Safari */'
  transform: rotate(90deg);  
}

.net2 {
  display: none;
}

.net3 {
  display: block;
}

var toggler = document.getElementsByClassName("net1");
var i;

for (i = 0; i < toggler.length; i++) {
  toggler[i].addEventListener("click", function() {
    this.parentElement.querySelector(".net2").classList.toggle("net3");
    this.classList.toggle("net1-down");
  });
}

<iframe src="https://www.netbax.net/tab/creation/tree-view.html" style="width: 550px; height:550px;" frameborder="0"></iframe>