( Waves ( ( are ( caused ( by wind ) ) ) . ) )
(ROOT (S (NP (NNS Waves)) (VP (VBP are) (VP (VBN caused) (PP (IN by) (NP (NN wind))))) (. .)))
Waves are caused by wind .
(ROOT (S (NP (NNP Ocean) (NNS waves)) (VP (VBP are) (ADVP (RB mainly)) (VP (VBN caused) (PP (IN by) (NP (NN wind))))) (. .)))