( ( Our Sun ) ( ( wobbles ( because ( of ( ( the gravity ) ( of ( ( the planets ) ( orbiting it ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Our) (NNP Sun)) (VP (VBZ wobbles) (PP (RB because) (IN of) (NP (NP (DT the) (NN gravity)) (PP (IN of) (NP (NP (DT the) (NNS planets)) (VP (VBG orbiting) (NP (PRP it)))))))) (. .)))
Our Sun wobbles because of the gravity of the planets orbiting it.
(ROOT (S (NP (NNS Planets)) (VP (VBP are) (VP (VBN held) (PP (IN by) (NP (NP (DT the) (NN force)) (PP (IN of) (NP (NN gravity))))) (PP (IN in) (NP (NP (JJ elliptical) (NNS orbits)) (PP (IN around) (NP (NN sun))))))) (. .)))