( ( For ( most ( of ( its life ) ) ) ) ( ( a star ) ( ( ( ( produces energy ) ( by ( fusing hydrogen ) ) ) ( to ( make helium ) ) ) . ) ) )
(ROOT (S (PP (IN For) (NP (NP (JJS most)) (PP (IN of) (NP (PRP$ its) (NN life))))) (NP (DT a) (NN star)) (VP (VBZ produces) (NP (NN energy)) (PP (IN by) (NP (NN fusing) (NN hydrogen))) (S (VP (TO to) (VP (VB make) (NP (NNP helium)))))) (. .)))
For most of its life a star produces energy by fusing hydrogen to make 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))))) (. .)))