bst_size :: Tree -> Int
bst_size t =
    case t of
        Empty -> 0
        (Node l _ r) -> (bst_size l) + (bst_size r) + 1

-- size of tree, using conversion to high level tree
bst_size :: Tree -> Int
bst_size t =
    case t of
        Empty -> 0
        (Node l _ r) -> (bst_size l) + (bst_size r) + 1

-- size of tree, using conversion to high level tree
bst_size t =
    case t of
        Empty -> 0
        (Node l _ r) -> (bst_size l) + (bst_size r) + 1

-- size of tree, using conversion to high level tree