objective c - How to make the NSButton above a NSButton? -

i'm having 2 nsbuttons. both button images. created [buttons] (http://i.stack.imgur.com/iyxie.png) problem star button located behind leaf button. how can bring front. (searching mac osx not ios.)
update: got during first mousehover , got during second mouse on

[starbutton removefromsuperview]; [self addsubview:starbutton positioned:nswindowabove relativeto:nil]; 

also, nsview supports method

 sortsubviewsusingfunction:context: 

implement sort views.. requires more code seems more clean.