This is a Christmas themed keycap. 

Mechanically bonded using snapfits and holds pretty well. 

There are two types of snap fits here, one inside the shell annular snap fit and 4 Cantilever Snap Fit outside.

I also did a lot of drop tests and yet the model doesn't come apart..

Assmebly is pretty simple. you fuirst pressfut the key then insert the bottom shell and then at last press the top shell hard on so that it fits in place.