[Haskell-beginners] A "show" error

Hi,  I'm trying to process on a tree with this function : f (Branch x (Branch y y1 y2) (Branch z z1 z2)) = (x,y,y1,y2,z,z1,z2) and my tree declaration is this :  data Tree = Empty | Branch Integer Tree Tree deriving (Show) And I'm getting this error :  Main> f (Branch 12 (Branch 15 Empty Empty) (Branch 28 Empty Empty)) ERROR - Cannot find "show" function for: *** Expression : f (Branch 12 (Branch 15 Empty Empty) (Branch 28 Empty Empty)) *** Of type    : (Integer,Integer,Tree,Tree,Integer,Tree,Tree) I'll be happy if you help me to get rid of this error..