asp.net TreeView控件绑定数据库显示信息

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Web.UI;
 using System.Web.UI.WebControls;
 using System.Data;
 using System.Data.SqlClient;
 using System.Configuration;

 public partial class _Default : System.Web.UI.Page
 {
     string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
     protected void Page_Load(object sender, EventArgs e)
     {
         SqlConnection conn = new SqlConnection(constr);
         conn.Open();
         string sql="select * from student";
         SqlDataAdapter da = new SqlDataAdapter(sql, conn);
         DataSet ds = new DataSet();
         da.Fill(ds,"student");
         //下面的方法动态添加了treeView的根节点和子节点
         TreeNode tree1 = new TreeNode("学生信息");//设置根节点
         this.TreeView1.Nodes.Add(tree1);
         for (int i = ; i < ds.Tables["student"].Rows.Count; i++)
         {
             TreeNode tree2 = new TreeNode(ds.Tables["student"].Rows[i][].ToString(), ds.Tables["student"].Rows[i][].ToString());
             tree1.ChildNodes.Add(tree2);//显示子节点
             for (int j = ; j < ds.Tables["student"].Columns.Count; j++)
             {
                 TreeNode tree3 = new TreeNode(ds.Tables["student"].Rows[i][j].ToString(), ds.Tables["student"].Rows[i][j].ToString());
                 tree2.ChildNodes.Add(tree3);
             }
         }
     }
     public void BindDataBase()
     {
         BindDataBase();
         TreeView1.ShowLines = true//显示连接父节点与子节点间的线条;
         TreeView1.ExpandDepth = ;//控件显示时所展开的层数
     }
 }

<configuration>
<connectionStrings>
<add name="constr" connectionString="server=.\sqlexpress;database=db2016;uid=sa;pwd=123;"/>
</connectionStrings>
<system.web>
<compilation debug="true" targetFramework="4.0" />
</system.web>

</configuration>