asp.net动态生成TreeView

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
public partial class left : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
       GetTreeView();
    }
    private void GetTreeView()
    {
        try
        {
            string connectionstring = "Server=(local);uid=sa;pwd=123456;database=web";//连接SQL数据库
            SqlConnection conn = new SqlConnection(connectionstring);
            string sql = "select * from menu where menu_level=1 and parent_id =0";//查询一级节点
            SqlDataAdapter adapter = new SqlDataAdapter(sql, conn);
            DataSet ds1 = new DataSet();
            adapter.Fill(ds1, "temp");
            DataTable table1 = ds1.Tables["temp"];//把读取的数据放入DATATABLE中
            TreeView1.Nodes.Clear();//建立根节点，遍历。
            foreach (DataRow dr1 in table1.Rows)
            {
                TreeNode root = new TreeNode();
  &