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 = 0; i < ds.Tables["student"].Rows.Count; i++)
        {
            TreeNode tree2 = new TreeNode(ds.Tables["student"].Rows[i][1].ToString(), ds.Tables["student"].Rows[i][1].ToString());
            tree1.ChildNodes.Add(tree2);//显示子节点
            for (int j = 0; 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 = 1;//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>