为了做个树型菜单，看了很多代码，但都没这个简洁，外国人写的，一起分享下：
1 先定义个JS：
2 CSS
body {
margin: 0px;
padding: 0;
font: 12px "Lucida Grande", Verdana, Arial, Helvetica, sans-serif;
background: #FFFFFF;
text-align: center;
}
ul{
margin: 0;
padding: 0;
list-style: none;
}
#treenav {
margin: 10px;
text-align: left;
}
#treenav ul li {
margin: 1px 0;
padding: 0;
font-size: 11px;
}
#treenav ul.expanded {
display: block;
}
#treenav ul.expanded,#treenav ul.collapsed {
margin: 5px 10px;
}
#treenav ul.collapsed {
display: none;
}
.expanded li,.collapsed li{
/*border-bottom: 1px dashed #CCCCCC;*/
width: 200px;
}
.listhead {
font-weight: bold;
display: block;
font-size: 12px;
color: #333333;
background: #F1F1F1;
padding: 3px;
width: 120px;
margin: 1px 0;
}
#treenav a {
text-decoration: none;
color: #666666;
}
#treenav a:hover {
color: #990000;
}
3 定义树型结构