It's pretty incredible that the treeview shown in the image below doesn't require any JavaScript at all, just CSS3! Take a look at this amazing CSS3 TreeView, specifically designed for use with Twitter BootStrap:

If you want to learn more about this innovative solution, check out the following link: .

If you are looking for a vertical version of the treeview inspired by Harsh's answer, here is a quick solution:

http://jsfiddle.net/2ftYe/

.tree li {
    margin: 0px 0;
    list-style-type: none;
    position: relative;
    padding: 20px 5px 0px 5px;
}

.tree li::before{
    content: '';
    position: absolute; 
    top: 0;
    width: 1px; 
    height: 100%;
    right: auto; 
    left: -20px;
    border-left: 1px solid #ccc;
    bottom: 50px;
}
.tree li::after{
    content: '';
    position: absolute; 
    top: 30px; 
    width: 25px; 
    height: 20px;
    right: auto; 
    left: -20px;
    border-top: 1px solid #ccc;
}
.tree li a{
    display: inline-block;
    border: 1px solid #ccc;
    padding: 5px 10px;
    text-decoration: none;
    color: #666;
    font-family: arial, verdana, tahoma;
    font-size: 11px;
    border-radius: 5px;
    -webkit-border-radius: 5px;
    -moz-border-radius: 5px;
}

/*Remove connectors before root*/
.tree > ul > li::before, .tree > ul > li::after{
    border: 0;
}
/*Remove connectors after last child*/
.tree li:last-child::before{ 
      height: 30px;
}

/*Hover effects*/
.tree li a:hover, .tree li a:hover+ul li a {
    background: #c8e4f8; 
    color: #000; 
    border: 1px solid #94a0b4;
}
/*Connector styles on hover*/
.tree li a:hover+ul li::after, 
.tree li a:hover+ul li::before, 
.tree li a:hover+ul::before, 
.tree li a:hover+ul ul::before{
    border-color:  #94a0b4;
}

Discovering a tree design using CSS3 can be an exciting journey. I came across this amazing code snippet that I found online:

HTML

<div class="tree">
  <ul>
    <li>
      <a href="#">Parent</a>
      <ul>
        <li>
          <a href="#">Child</a>
          <ul>
            <li>
              <a href="#">Grand Child</a>
            </li>
          </ul>
        </li>
        <li>
          <a href="#">Child</a>
          <ul>
            <li><a href="#">Grand Child</a></li>
            <li>
              <a href="#">Grand Child</a>
              <ul>
                <li>
                  <a href="#">Great Grand Child</a>
                </li>
                <li>
                  <a href="#">Great Grand Child</a>
                </li>
                <li>
                  <a href="#">Great Grand Child</a>
                </li>
              </ul>
            </li>
            <li><a href="#">Grand Child</a></li>
          </ul>
        </li>
      </ul>
    </li>
  </ul>
</div>

CSS

* {margin: 0; padding: 0;}

.tree ul {
  padding-top: 20px; position: relative;

  transition: all 0.5s;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
}

.tree li {
  float: left; text-align: center;
  list-style-type: none;
  position: relative;
  padding: 20px 5px 0 5px;

  transition: all 0.5s;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
}

/*We will use ::before and ::after to draw the connectors*/

.tree li::before, .tree li::after{
  content: '';
  position: absolute; top: 0; right: 50%;
  border-top: 1px solid #ccc;
  width: 50%; height: 20px;
}
.tree li::after{
  right: auto; left: 50%;
  border-left: 1px solid #ccc;
}

/*We need to remove left-right connectors from elements without 
any siblings*/
.tree li:only-child::after, .tree li:only-child::before {
  display: none;
}

/*Remove space from the top of single children*/
.tree li:only-child{ padding-top: 0;}

/*Remove left connector from first child and 
right connector from last child*/
.tree li:first-child::before, .tree li:last-child::after{
  border: 0 none;
}
/*Adding back the vertical connector to the last nodes*/
.tree li:last-child::before{
  border-right: 1px solid #ccc;
  border-radius: 0 5px 0 0;
  -webkit-border-radius: 0 5px 0 0;
  -moz-border-radius: 0 5px 0 0;
}
.tree li:first-child::after{
  border-radius: 5px 0 0 0;
  -webkit-border-radius: 5px 0 0 0;
  -moz-border-radius: 5px 0 0 0;
}

/*Time to add downward connectors from parents*/
.tree ul ul::before{
  content: '';
  position: absolute; top: 0; left: 50%;
  border-left: 1px solid #ccc;
  width: 0; height: 20px;
}

.tree li a{
  border: 1px solid #ccc;
  padding: 5px 10px;
  text-decoration: none;
  color: #666;
  font-family: arial, verdana, tahoma;
  font-size: 11px;
  display: inline-block;

  border-radius: 5px;
  -webkit-border-radius: 5px;
  -moz-border-radius: 5px;

  transition: all 0.5s;
  -webkit-transition: all 0.5s;
  -moz-transition: all 0.5s;
}

/*Time for some hover effects*/
/*We will apply the hover effect the the lineage of the element also*/
.tree li a:hover, .tree li a:hover+ul li a {
  background: #c8e4f8; color: #000; border: 1px solid #94a0b4;
}
/*Connector styles on hover*/
.tree li a:hover+ul li::after, 
.tree li a:hover+ul li::before, 
.tree li a:hover+ul::before, 
.tree li a:hover+ul ul::before{
  border-color:  #94a0b4;
}

PS: Aside from the code itself, I was impressed by the interactive display on the website showcasing the tree structure in action.

If you're looking for an expandable/collapsible version of the treeview inspired by Vitaliy Bychik's answer, I've got a time-saving solution for you!

Check out this link to see it in action.

$(function () {
    $('.tree li').hide();
    $('.tree li:first').show();
    $('.tree li').on('click', function (e) {
        var children = $(this).find('> ul > li');
        if (children.is(":visible")) 
            children.hide('fast');
        else 
            children.show('fast');
        e.stopPropagation();
    });
});

If you're looking for a reliable Treeview jQuery plugin, consider exploring the options available at

For a more advanced view, be sure to check out jquery-treetable as well: