[Haskell-beginners] Empty or Tree?

[bahadýr altan]

Hello everyone. I'm trying to write a code which works on binary trees. When I write code like this  with a tree with empty nodes :

data Tree  =  Empty | Node  Integer Tree Tree

function Node a (Node b Empty Empty)  (Node c Empty Empty)

it works fine. 
But when I try to create a more generic code like this  which could  work with trees who don't have empty nodes in grandchild level : 

function Node a (Node b Tree Tree)  (Node c Tree Tree ) 


I get this error : Undefined data constructor "Tree"

Can you help me with creating more generic code please?
Thanks
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