( ( ( ( ( ( Most ( surface waves ) ) ( are ( caused ( by wind ) ) ) ) , ) but ) ( ( the ( wind source ) ) ( ( need not ) ( be nearby ) ) ) ) . )
(ROOT (S (S (NP (JJS Most) (NN surface) (NNS waves)) (VP (VBP are) (VP (VBN caused) (PP (IN by) (NP (NN wind)))))) (, ,) (CC but) (S (NP (DT the) (NN wind) (NN source)) (VP (VBP need) (RB not) (VP (VB be) (ADVP (RB nearby))))) (. .)))
Most surface waves are caused by wind, but the  wind source need not be nearby.
(ROOT (S (NP (JJS Most) (NN ocean) (NNS waves)) (VP (VBP are) (VP (VBN caused) (PP (IN by) (NP (NN wind))))) (. .)))