code: function(li,maxLevel) {
        this.expandElement(li);
        var sub = Dom.getChildrenBy(li, function(c) {return c.tagName == "UL";})[0].childNodes;
        for(var j = 0 ; j < sub.length ; j++) {
           var s = sub[j];
           if(Dom.hasClass(s,"collapsed") && maxLevel != 0) {
              this.expandBranch(s,maxLevel-1);
           }
        }
     }
docs: Expand a branch given a li element
  @param {HTMLElement} li
  @param {Integer} maxLevel