//数据绑定
    private void TreeBind(DropDownList ddl)
    {
        DataTable dt = dal.GetList(" parent_id=0 ").Tables[0];
        ddl.Items.Clear();
        ddl.Items.Add(new ListItem("请选择...", "0"));
        foreach (DataRow dr in dt.Rows)
        {
            ddl.Items.Add(new ListItem(dr["name"].ToString(), dr["id"].ToString()));
        }
    }