对数据进行递归排序以树状显示

源数据：
id  上级id
1    0
2    0
11   1
21   1
111  11

树状后显示：
1
--11
---111
2
--21

#region 自定义方法

    #region bind TypeID
    private void fn_Bind_ddl_Type()
    {
        DataSet ds;

        BLL.MyTypeInfo bll_Type = new BLL.MyTypeInfo();
        ds = bll_Type.SelectAllTypeForChoose();

        this.ddl_Type.Items.Clear();
        if (ds != null && ds.Tables.Count > 0 && ds.Tables[0].Rows.Count > 0)
        {
            DataTable dtPara = ds.Tables[0];
            DataTable dtTree = new DataTable();
            dtTree = dtPara.Clone();
            fn_ChangeToTree(ref dtTree, dtPara, 0, "0");//从顶级开始递归遍历

            this.ddl_Type.DataSource = dtTree;
            this.ddl_Type.DataTextField = dtTree.Columns[1].ToString();
            this.ddl_Type.DataValueField = dtTree.Columns[0].ToString();
            this.ddl_Type.DataBind();
        }
        this.ddl_Type.Items.Insert(0, new ListItem("", "0"));
    }
    #endregion

    #region 将信息 整理成树状
    private void fn_ChangeToTree(ref DataTable dtTree, DataTable dtPara, int intLevel, string strParentTypeID)
    {
        intLevel++;
        string strLeftPre = "";
        if (intLevel > 1)
        {
            strLeftPre = "|" + strLeftPre.PadLeft(intLevel * 2, '-');
        }
        DataTable dt1 = new DataTable();//当前级别
        dt1 = dtPara.Clone();
        DataTable dt2 = new DataTable();//下一级
        dt2 = dtPara.Clone();

        for (int i = 0; i < dtPara.Rows.Count; i++)
        {
            DataRow dr = dtPara.Rows[i];
            string strRowParentType = dr["ParentType"].ToString();
            if (strRowParentType == strParentTypeID)
            {
                dt1.Rows.Add(dr.ItemArray);
            }
            else
            {
                dt2.Rows.Add(dr.ItemArray);
            }
        }

        for (int j = 0; j < dt1.Rows.Count; j++)
        {
            DataRow dr = dt1.Rows[j];

            dr["TypeName"] = strLeftPre + dr["TypeName"].ToString();
            dtTree.Rows.Add(dr.ItemArray);
            string strRowParentType = dr["TypeID"].ToString();
            fn_ChangeToTree(ref dtTree, dt2, intLevel, strRowParentType);
        }
    }
    #endregion

    #endregion