Tree implementations in Haskell

bintree.hs

import Data.Maybe
import Data.Functor

data Tree a = Node a (Maybe (Tree a)) (Maybe (Tree a)) 
    deriving Show

instance Functor Tree where
    fmap f (Node x left right) = Node (f x) (left >>= return . fmap f) (right >>= return . fmap f)

main = print $ fmap (2*) (Node 2 (Just $ Node 10 Nothing Nothing) Nothing)

tree.hs

import Data.Maybe
import Data.Functor


data Tree a = Tree a [Tree a] 
    deriving Show

instance Functor Tree where 
    fmap f (Tree x children) = Tree (f x) (fmap (fmap f) children)

main :: IO ()
main = print $ fmap (2*) (Tree 1 [Tree 3 [Tree 4 [], Tree 5 []]])