( Uranus ( ( is ( ( a ball ) ( of ( ( ( mostly hydrogen ) and ) helium ) ) ) ) . ) )
(ROOT (S (NP (NNS Uranus)) (VP (VBZ is) (NP (NP (DT a) (NN ball)) (PP (IN of) (NP (NP (RB mostly) (NN hydrogen)) (CC and) (NP (NNP helium)))))) (. .)))
Uranus is a ball of mostly hydrogen and helium.
(ROOT (S (NP (NNP Saturn)) (VP (VBZ is) (VP (VBN made) (ADVP (RB mostly)) (PP (IN of) (NP (NN helium) (CC and) (NN hydrogen))))) (. .)))