*Test.AllStarTests> parse ['a', 'b', 'c'] (NT 'S') atnEnv
(Just True, Node 'S' [Node 'A' [Leaf 'a', Node 'A' [Leaf 'b']], Leaf 'c'])

*Test.AllStarTests> parse ['b', 'd'] (NT 'S') atnEnv
(Just True, Node 'S' [Node 'A' [Leaf 'b'], Leaf 'd'])

*Test.AllStarTests> parse ['a', 'a', 'a', 'a', 'b', 'c'] (NT 'S') atnEnv
(Just True, Node 'S' [Node 'A' [Leaf 'a', Node 'A' [Leaf 'a', Node 'A' [Leaf 'a', Node 'A' [Leaf 'a', Node 'A' [Leaf 'b']]]]], Leaf 'c'])