Well, I found out that the argument only works for the subpage of a page, and not for the subsubpage of a subpage.
main-1
subpage-1
subpage-2
subsubpage-1
subpage-3
main-2
subpage-4
subpage-5
When I’m at subsubpage-1, the parent page id returned to be the subpage-2. Is there any ways to make return the parent page id to be the global parent page, in this case, the main-1 page?