function select_all()
    {     
//       var a = document.getElementsByTagName("input");
//       var b = document.getElementsById("TreeViewCategory");
       if (document.getElementById("selectall").value=="展开")
       {
           document.getElementsById("TreeViewCategory").setattribute("expanded","true");
           document.getElementById("selectall").value="收缩";
       }
       else
       {
           document.getElementsById("TreeViewCategory").setattribute("expanded","false");
           document.getElementById("selectall").value="收缩"
       }
    } 
请帮忙修改下 TreeView 展开 收缩的代码