Hi, 

I was writing some code for Tree. 

1 : data Tree a = NULL | Node a (Tree a) (Tree a)   works fine. But,

2  : data Tree a = NULL | Tree a (Node a) Tree a does not work. GHCI says Not in scope " type constructor or class 'Node'.   

Why is 2 declaration not valid though second definition looks much more closer to what a binary tree actually means ?