( ( ( ( ( Certainly ( , ( birth ( ( can often ) ( require effort ) ) ) ) ) , ) but ) ( sometimes ( it ( 's ( nice ( to ( use ( ( the analogy ) ( of ( ( floating down ) ( a ( gentle ( mountain stream ) ) ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (ADVP (RB Certainly)) (, ,) (NP (NN birth)) (VP (MD can) (ADVP (RB often)) (VP (VB require) (NP (NN effort))))) (, ,) (CC but) (S (ADVP (RB sometimes)) (NP (PRP it)) (VP (VBZ 's) (ADJP (JJ nice) (S (VP (TO to) (VP (VB use) (NP (NP (DT the) (NN analogy)) (PP (IN of) (S (VP (VBG floating) (PRT (RP down)) (NP (DT a) (JJ gentle) (NN mountain) (NN stream)))))))))))) (. .)))
Certainly, birth can often require effort, but sometimes it's nice to use the analogy of floating down a gentle mountain stream.
(ROOT (S (NP (NNS Streams)) (ADVP (RB often)) (VP (VBP start) (PP (IN in) (NP (NNS mountains)))) (. .)))