Treeview Node Related data

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace Treeview_Node__Related_data
{
public partial class Form1 : Form
{
string ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["dsn"];
OleDbCommand com;
OleDbDataAdapter oledbda;
DataSet ds;
string str;

public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
treeView1.Nodes.Add("Please select any Name");
OleDbConnection con = new OleDbConnection(ConnectionString);
con.Open();
str = "select * from student";
com = new OleDbCommand(str, con);
OleDbDataReader reader = com.ExecuteReader();
while (reader.Read())
{
treeView1.Nodes.Add(reader["sname"].ToString());
}
reader.Close();
con.Close();
}

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
OleDbConnection con = new OleDbConnection(ConnectionString);
con.Open();
str = "select * from student where sname='" + treeView1.SelectedNode.Text + "'";
com = new OleDbCommand(str, con);
oledbda = new OleDbDataAdapter(com);
ds = new DataSet();
oledbda.Fill(ds, "student");
dataGridView1.DataMember = "student";
dataGridView1.DataSource = ds;
con.Close();
}
}
}