C#递归在dropdownlist显示树状

/// <summary>
    /// 绑定文件分类
    /// </summary>
    public void bind()
    {
        //获取数据集
        DataSet ds = new DataSet();
        ds = ec.ExecuteSelectCmmond("select * from t_Column where U_UserID='" + HttpContext.Current.Request.Cookies["NameID"].Value + "'", ds);
        BindingCWAList(DropDownList1, ds);
    }
    private void BindingCWAList(DropDownList ddlID, DataSet ds) //ddlID是DropDownList控件的ID
    {
        DropDownList1.Items.Clear();
        //此处创建顶极分类,Value=0(如不需要，可以删除此行)
        ddlID.Items.Add(new ListItem("请选择目录", "0"));
        InitList(ddlID, 0, ds, "");
    }

    private void InitList(DropDownList ddlID, int parentID, DataSet catagoryDS, string indent)
    {
        //Select后边的是DataSet里面的列名
        System.Data.DataRow[] currRows = catagoryDS.Tables[0].Select("ColumnFatherld=" + parentID.ToString(), "ColumnFatherld ASC");
        int count = currRows.Length;
        DataRow catagoryRow;
        for (int i = 0; i < count; i++)
        {
            catagoryRow = currRows[i];
            System.Web.UI.WebControls.ListItem item = new System.Web.UI.WebControls.ListItem(indent + catagoryRow　　　　  ["ColunmnName"].ToString(), catagoryRow["ColumnId"].ToString());
            ddlID.Items.Add(item);
            InitList(ddlID, Int32.Parse(catagoryRow["ColumnId"].ToString()), catagoryDS, indent + "……");
        }
    }