zipTree :: (a -> b -> c) -> T.Tree a -> T.Tree b -> T.Tree c
zipTree f t1 t2 = Node {
    rootLabel = f (rootLabel t1) (rootLabel t2)
  , subForest = zipSubForest f (subForest t1) (subForest t2)
  }
zipTree :: (a -> b -> c) -> T.Tree a -> T.Tree b -> T.Tree c
zipTree f t1 t2 = Node {
    rootLabel = f (rootLabel t1) (rootLabel t2)
  , subForest = zipSubForest f (subForest t1) (subForest t2)
  }
zipTree f t1 t2 = Node {
    rootLabel = f (rootLabel t1) (rootLabel t2)
  , subForest = zipSubForest f (subForest t1) (subForest t2)
  }