( ( Like Jupiter ) ( , ( Saturn ( ( ( is mostly ) ( ( hydrogen and ) helium ) ) . ) ) ) )
(ROOT (S (PP (IN Like) (NP (NNP Jupiter))) (, ,) (NP (NNP Saturn)) (VP (VBZ is) (ADVP (RB mostly)) (NP (NP (NN hydrogen)) (CC and) (NP (NNP helium)))) (. .)))
Like Jupiter, Saturn is 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))))) (. .)))