protected DataSet PDataset(string select_statement)
{
            SqlConnection _con = new SqlConnection("DataSource(Local);         database =DATABASE NAME ; UserID=sa;Password=******");
            SqlDataAdapter ad = new SqlDataAdapter(select_statement, _con);
            DataSet ds = new DataSet();
            ad.Fill(ds);
            _con.Close();
            return ds;
}


 public void Load_tree()
 {
            DataSet PrSet = PDataset("SELECT * FROM tree");
            treeView1.Nodes.Clear();
            foreach (DataRow dr in PrSet.Tables[0].Rows)
            {
                if ((int)dr["ParentID"] ==  0 )
                {
                    TreeNode tnParent = new TreeNode();
                    tnParent.Text = dr["Name"].ToString();
                    string value = dr["IID"].ToString();
                    tnParent.Expand();
                    treeView1.Nodes.Add(tnParent);
                    FillChild(tnParent, value);
                 }
             }
}

        public int FillChild(TreeNode parent,string IID)
        {

            DataSet ds = PDataset("SELECT * FROM tree WHERE ParentID =" + IID );
            if (ds.Tables[0].Rows.Count > 0)
            {

                foreach (DataRow dr in ds.Tables[0].Rows)
                {
                    TreeNode child = new TreeNode();
                    child.Text = dr["Name"].ToString().Trim();
                    string temp = dr["IID"].ToString();
                    child.Collapse();
                    parent.Nodes.Add(child);
                    FillChild(child, temp);
                }
                return 0;
            }
            else 
            {
                return 0;
            }
                                                          
        }