Coolite 

<West Collapsible="true" Split="true" MaxWidth="200px">
        <ext:TreePanel ID="tpnNavigator" runat="server" AutoHeight="True" RootVisible="False" Width="200px" Icon="ApplicationViewList">
               <DirectEvents>
                     <Click OnEvent="tpnNavigator_Click">
                           <ExtraParams>
                                  <ext:Parameter Name="paraFunID" Value="node.id" Mode="Raw" />
                           </ExtraParams>
                     </Click>
               </DirectEvents>
        </ext:TreePanel>
</West>

    protected void tpnNavigator_Click(object sender, DirectEventArgs e)
    {
        //string strFunID = tpnNavigator.ActiveTab.ID;   SEEMS CANN'T GET THE RIGHT VALUE!!!
        string strFunID = e.ExtraParams["paraFunID"].ToString();
        bool Existed = false;
        //tpList is the ID of the tabpanel control
        foreach (Ext.Net.Component li in tpList.Items)
        {
            if (li.ID == strFunID)
            {
                Existed = true;
                break;
            }
        }
        if (Existed)
        {
            tpList.SetActiveTab(strFunID);
        }
        else
        {
            SysFunctions objFun = SysFunctions.SelectByFunID(strFunID);
            Ext.Net.Panel pnl = new Ext.Net.Panel();
            pnl.ID = "TAB_" + strFunID;
            pnl.Title = objFun.FunName;
            pnl.AutoLoad.Url = objFun.FunURL;
            pnl.AutoLoad.Mode = LoadMode.IFrame;
            pnl.Render(tpList, RenderMode.AddTo);
            //pnl.AddTo(tpList);
            tpList.SetActiveTab(strFunID);
        }
    }