2,categories.aspx.cs

private void Page_Load(object sender, System.EventArgs e)
  {
   string sql=@"select categoryname as Text,'products.aspx?catid='+ltrim(str(categoryid)) as TreeNodesrc
    from categories as TreeNode for xml auto ,xmlData " ;
   SqlConnection sqlConn=new SqlConnection("Server=dbm-1;Uid=sa;pwd=;DataBase=Northwind");
   SqlCommand  com=new  SqlCommand (sql,sqlConn);
   DataSet ds=new DataSet();
   sqlConn .Open();
    ds.ReadXml(com.ExecuteXmlReader(),XmlReadMode.Fragment );
   sqlConn.Close();
   sqlConn=null;

   ds.DataSetName ="TREENODES";
   ds.WriteXml(Response.OutputStream );

  }