I found that because I placed the code  in a command box, then when I
press the command box to display only level1, it worked as
expected. At this time, I lost the cursor. Then if I want to click
the original level  1, 2 ,3 button provided by Excel in the left side
of the spreadsheet, I need to do it twice: first time to bring
cursor's attention back to spreadsheet, second time to do the normal
fold/unfold job. I sloved this problem by adding something like
--
Cells(currentRow, currentCol).Select
--
at the very end of the code in command box to bring cursor's
attention back. It is OK now.

But, I just wonder must I do this extra step? Shouldn't Excel do
that for us?