[Haskell-beginners] Empty or Tree?

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