import Control.Monad.State.Strict

data Node = Node [Node] deriving Show

mknode :: Int -> State Int Node
mknode 1 = do
  modify (1+)
  return $ Node []

mknode (k+1) = do
  modify (1+)
  p1 <- mknode k
  p2 <- mknode k
  return $ Node [p1, p2]

main = print $ runState (mknode 10) 0