Delphi与SQL 2000结合生成Treeview的问题

下面是本人写的代码：
unit untDepttree;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ComCtrls, StdCtrls, DB, ADODB;

type
  TfrmDepttree = class(TForm)
    GroupBox1: TGroupBox;
    TreeView_deptlist: TTreeView;
    Button_ok: TButton;
    Button_cancel: TButton;
    ADODataSet1: TADODataSet;
    procedure FormCreate(Sender: TObject);
  private
    treenodedata:array[1..3000] of string;
    cnt:Integer;
  public
    { Public declarations }
    procedure Insertnodetotree(node:TTreeNode; upcode:string);
  end;

var
  frmDepttree: TfrmDepttree;

implementation

uses DBModule;

{$R *.dfm}

procedure TfrmDepttree.FormCreate(Sender: TObject);
begin
  TreeView_deptlist.Items.Clear;
  ADODataSet1.Open;
  Insertnodetotree(nil,'0');
end;

procedure TfrmDepttree.Insertnodetotree(node: TTreeNode; upcode: string);
var
  id,deptname,preid:string;
  newnode:TTreeNode;
  i:integer;
  j : integer;
begin
  ADODataSet1.First; <