haskell very simple tree

Tree.hs

module Tree where

data Tree v = EmptyTree
          | Node v (Tree v) (Tree v)
            deriving  Show            
                      
singleton value = Node value EmptyTree EmptyTree             

--map f EmptyTree = EmptyTree
--map f Node v left right = Node (f v) (map f left) (map f right)

instance Functor Tree where
  fmap f EmptyTree = EmptyTree
  fmap f (Node v left right) = Node (f v) (fmap f left) (fmap f right)