what is the best approach to implement Tree View?
<ul>
        <li>Level 1 a
            <ul>
                <li>Level 2 a</li>
                <li>Level 2 b
                    <ul>
                        <li>Level 3 a</li>
                        <li>Level 3 b</li>
                    </ul>
                </li>
            </ul>
        </li>
        <li>Level 1 b</li>
    </ul>

<li onClick="redicrectPage(url)">

<ul class="menu">
    <li><a href="#">Level 1 a</a>
        <ul>
            <li><a href="#">Level 2 a</a></li>
            <li><a href="#">Level 2 b</a>
                <ul>
                    <li><a href="#">Level 3 a</a></li>
                    <li><a href="#">Level 3 b</a></li>
                </ul>
            </li>
        </ul>
    </li>
    <li><a href="#">Level 1 b</a></li>
</ul>​

* { font-family: tahoma, sans-serif; font-size: 10pt; }
a { text-decoration: none; color: #fff; display: block; }
ul { display: none; }
ul.menu, li:hover > ul { display: block; }
li > ul { position: absolute; top: 25%; left: 100%; margin-left: -1em;
   box-shadow: -1px 1px 1px rgba(0,0,0,0.5); z-index: 1000; }
li { position: relative; padding: 0.1em 0.5em; width: 100px; background: silver;
   box-shadow: -1px 1px 1px rgba(0,0,0,0.5); margin: 1px 1px 0; }
li:hover { background-color: #333; }
li:hover > a { color: #FAFAFE; }