无限级分根据当前Id读取下级Id

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Configuration;
using System.Data.SqlClient;
public partial class nextclassid : System.Web.UI.Page
{
    protected static string connectionString = ConfigurationManager.AppSettings["ConnStr"].ToString();

    protected void Page_Load(object sender, EventArgs e)
    {
        int classid = Convert.ToInt32(Request.QueryString["id"]);
        DataList1.DataSource = GetListClass(classid);
        DataList1.DataBind();
    }
    public DataTable GetListClass(int ClassId)
    {
        SqlConnection Conn = new SqlConnection(connectionString);
        Conn.Open();
        SqlDataAdapter sda = new SqlDataAdapter();
        sda.SelectCommand = new SqlCommand("select * from ArticleClass", Conn);
        //DataSet ds = new DataSet();
        //sda.Fill(ds, "ArticleClass");
        //DataTable DT = new DataTable();
        //DT = (DataTable)ds.Tables["ArticleClass"];
        DataTable DT = new DataTable();
        sda.Fill(DT);
        DataRow myrow;
        DataTable mytab = new DataTable();
        mytab.Columns.Add("Id");
        mytab.Columns.Add("Title");
        mytab.Clear();
        for (int i = 0; i < DT.Rows.Count; i++)
        {
            if (ClassId == (int)DT.Rows[i]["ParentId"])
            {
                myrow = mytab.NewRow();
                myrow[0] = DT.Rows[i]["Id"];
                myrow[1] = DT.Rows[i]["Title"];
                mytab.Rows.Add(myrow);
                myrow.AcceptChanges();
            }
        }
        if (mytab.Rows.Count == 0) mytab = GetListClass(0);
        return mytab;

    }
}