( ( A wheel ) ( ( is ( ( a type ) ( of ( simple machine ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN wheel)) (VP (VBZ is) (NP (NP (DT a) (NN type)) (PP (IN of) (NP (JJ simple) (NN machine))))) (. .)))
A wheel is a type of simple machine.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD six) (NNS types) (NNS types)) (PP (IN of) (NP (JJ simple) (NNS machines))))) (. .)))