Create a sumtree given the value of root node and depth of tree

sumtree.hs

data Tree a = NullNode | Node a (Tree a) (Tree a)

instance (Show a) => Show (Tree a) where
  show NullNode = ""
  show (Node x NullNode NullNode) = show x
  show (Node x l r) = show x ++ "(" ++ show l ++ " " ++ show r ++ ")"


sumtree :: Int -> Int -> Tree Int
sumtree rootVal depth
  | depth == 1 = Node rootVal NullNode NullNode
  | otherwise = Node rootVal (sumtree leftSum (depth - 1)) (sumtree rightSum (depth - 1))
  where leftSum = if even rootVal
                  then if depth == 2 then rootVal `div` 2 else rootVal `div` 4
                  else if depth == 2 then rootVal `div` 2 else (rootVal -1) `div` 4
        rightSum = if even rootVal
                   then if depth == 2 then rootVal - leftSum else (rootVal `div` 2) - leftSum
                   else if depth == 2 then rootVal - leftSum else (rootVal `div` 2) - leftSum + 1