如何用treeview打开相应窗体？

主要就是实现跟菜单一样的功能，点击其子项，会弹出个窗口
我的代码是procedure Tmainform.TreeView1Click(Sender: TObject);
var flag:integer;

begin
flag:=treeview1.Items.Item.SelectedIndex;
     case flag of
      flag:=1:        zengjiayonghu.Show;
      flag:=2:        mimaform.Show;
      flag:=3:       if messagebox(handle,'是否真的退出系统','提示',mb_IconQuestion + mb_OkCancel)=idok then
                                 close;
      flag:=4:        fangjianshezhi.Show;
      flag:=5:        sushefenpei.Show;
      flag:=6:        fangjianchaxun.Show;
      flag:=7:        laifangdengji.Show;
      flag:=8:         likaidengji.Show;
      flag:=9:         laifangjiluchaxun.Show;
      flag:=10:         weishengpingbijilu.Show;
      flag:=11:         pingbijieguochaxun.Show;
      flag:=12:         weijichuli.Show;
      flag:=13:         weijichaxun.Show;
      flag:=14:          group.Show;
      end;



end;但第一句有错，请大家帮帮忙啦