/// <summary>
        /// 樹形DRP
        /// </summary>
        /// <param name="list">ddl控件</param>
        /// <param name="m_DS">數據源</param>
        /// <param name="m_Text">默認顯示</param>
        /// <param name="m_UpFieldId">父ID</param>
        /// <param name="m_FieldId">ID</param>
        /// <param name="m_FieldText">顯示內容</param>
        public static void BindTreeDrp(DropDownList list, System.Data.DataSet m_DS, string m_Text, string m_UpFieldId, string m_FieldId, string m_FieldText)
        {
            System.Data.DataTable dt = m_DS.Tables[0];

            list.Items.Clear();
            if (!string.IsNullOrEmpty(m_Text)) list.Items.Add(new ListItem(m_Text, ""));

            System.Data.DataRow[] drs = dt.Select(m_UpFieldId + "=0");

            foreach (System.Data.DataRow dr in drs)
            {
                string bid = dr[m_FieldId].ToString();
                string bussesname = dr[m_FieldText].ToString();
                list.Items.Add(new ListItem(bussesname, bid));
                int chrid = int.Parse(bid);
                string blank = "　";
                BindNode(list, m_UpFieldId, m_FieldId, m_FieldText, chrid, dt, blank);//绑定子节点
            }

        }

 private static void BindNode(System.Web.UI.WebControls.DropDownList list, string m_UpFieldID, string m_FieldID, string m_FieldText, int parentid, System.Data.DataTable dt, string blank)
        {
            System.Data.DataRow[] drs = dt.Select(m_UpFieldID + "= " + parentid);

            foreach (System.Data.DataRow r in drs)
            {
                string nodeid = r[m_FieldID].ToString();
                StringBuilder text = new StringBuilder();
                text.Append(blank);
                text.Append(r[m_FieldText].ToString());

                list.Items.Add(new ListItem(text.ToString(), nodeid));
                int sonparentid = System.Int32.Parse(nodeid);
                StringBuilder blank2 = new StringBuilder();
                blank2.Append(blank);
                blank2.Append("　");
                BindNode(list, m_UpFieldID, m_FieldID, m_FieldText, sonparentid, dt, blank2.ToString());
            }
        }

------解决方案--------------------
一个无限递归