DropDownList弹出树状图

using System;
using System.Collections.Generic;
using System.Web;
using System.Data;
using System.Data.OleDb;
using System.Web.UI.WebControls;
/// <summary>
///Common 的摘要说明
/// </summary>
public class Common
{
 public Common()
 {
  //
  //TODO: 在此处添加构造函数逻辑
  //
 }
    //获取第一个父类
    public static List<ProductFLEntiy> GetList()
    {
        List<ProductFLEntiy> list = new List<ProductFLEntiy>();
        using (OleDbDataReader ord = SqlHelper.ExecuteReader("select * from productfl where ParentID=0"))
        {
            while (ord.Read())
            {
                ProductFLEntiy info = new ProductFLEntiy();
                info.ID = (int)ord["ID"];
                info.ParentID = (int)ord["ParentID"];
                info.ProFLName = ord["ProFLName"].ToString();
                list.Add(info);
            }
        }
        return list;
    }
    //通过父类ID来获取相关信息
    public static List<ProductFLEntiy> GetParentIDList(int ParentID)
    {
        List<ProductFLEntiy> list = new List<ProductFLEntiy>();
        using (OleDbDataReader ord = SqlHelper.ExecuteReader("select * from productfl where ParentID="+ParentID))
        {
            while (ord.Read())
            {
                ProductFLEntiy info = new ProductFLEntiy();
                info.ID = (int)ord["ID"];
                info.ParentID = (int)ord["ParentID"];
                info.ProFLName = ord["ProFLName"].ToString();
                list.Add(info);
            }
        }
        return list;
    }
    public static void BindClass(DropDownList dro)
    {
        List<ProductFLEntiy> list = GetList();
        foreach (ProductFLEntiy model in list)
        {
            ListItem li = new ListItem();
            li.Text = "╋" + model.ProFLName;
            li.Value = model.ID.ToString();
            dro.Items.Add(li);
            BindChild(dro,model.ID, "├──");
        }
    }

    public static void BindChild(DropDownList dro,int ParentID, string separator)
    {
        List<ProductFLEntiy> list = GetParentIDList(ParentID);
        foreach (ProductFLEntiy model in list)
        {
            ListItem li = new ListItem();
            li.Text = separator + model.ProFLName;
            li.Value = model.ID.ToString();
            dro.Items.Add(li);
            string separator_ = separator + "───";
            BindChild(dro,model.ID,separator_);
        }
    }
}

public class ProductFLEntiy
{
 public ProductFLEntiy()
 {
  //
  //TODO: 在此处添加构造函数逻辑
  //
 }
    private int _ID;

    public int ID
    {
        get { return _ID; }
        set { _ID = value; }
    }
    private int _ParentID;

    public int ParentID
    {
        get { return _ParentID; }
        set { _ParentID = value; }
    }
    private string _ProFLName;

    public string ProFLName
    {
        get { return _ProFLName; }
        set { _ProFLName = value; }
    }
}