Why is the 'dancing zombies' button not showing?

So I grew the tree of wisdom up to 520 feet and at 500 it said that i could press the dancing zombies button in the menu. So i went onto 1-7 and went into the menu; pressed the glasses but couldn't find anything related to dancing zombies so if this is just a visual bug and its not showing please fix this. But unless it needs disco zombie tell me so.