Populate TreeView from Database using C#

        public DataTable LoadDataTable(string RefId)
        {
            string cs = "Your Connection String Here"; //"server=SharpCoders;UID=sa;password=sa1223;database=POS";
            string query = "SELECT * from Sales where ReferenceID ='" + RefId + "' order by CustomerID ASC ";
            DataTable dataTable = new DataTable();
            SqlDataAdapter dAdapter = new SqlDataAdapter(query, cs);
            dAdapter.Fill(dataTable);
            return dataTable;
        }
        public TreeView loadTreeMenu(TreeView tvMenu, DataTable dtSale)
        {
            if (dtSale.Rows.Count > 0)
            {
                foreach (DataRow drRec in dtSale.Rows)
                {
                    TreeNode ParentNode = new TreeNode();
                    ParentNode.Text = drRec["CustomerNameSales"].ToString();
                    tvMenu.Nodes.Add(ParentNode);
                    loadTreeSubMenu(ref ParentNode, drRec["CustomerID"].ToString(), dtSale);
                }
            }
            return tvMenu;
        }
        private void loadTreeSubMenu(ref TreeNode ParentNode, string ParentId, DataTable dtSale)
        {
            DataTable dtChildRecords = this.LoadDataTable(ParentId);
            foreach (DataRow dRow in dtChildRecords.Rows)
            {
                TreeNode child = new TreeNode();
                child.Text = dRow["CustomerNameSales"].ToString();
                ParentNode.Nodes.Add(child);
                //Recursion
                loadTreeSubMenu(ref child, dRow["CustomerID"].ToString(), dtSale);
            }
        }
        private void button5_Click(object sender, EventArgs e)
        {
            treeView1.Nodes.Clear();
            loadTreeMenu(treeView1, LoadDataTable(textBox1.Text));
        }