How to make something similar a SlideView with mask

Hi everyone.
I have a small game with many levels, so I need a menu board to allow user to choice level.
I have two menu, one with buttons from 1->10, and one with buttons from 11-20, and only one can show at same time. I insert them to MenuLayer (CCLayer). I want to set something like “mask” to my MenuLayer, show only a part of this can be “visible”. How to do it?