( ( The ( gas bubble ) ) ( ( helps ( to ( ( ( seal and ) flatten ) ( the ( hole postoperatively ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN gas) (NN bubble)) (VP (VBZ helps) (S (VP (TO to) (VP (VB seal) (CC and) (VB flatten) (NP (DT the) (NN hole) (NN postoperatively)))))) (. .)))
The gas bubble helps to seal and flatten the hole postoperatively.
(ROOT (S (NP (NNP Gas) (NN bubble) (NNS holes)) (VP (VBZ helps) (NP (NP (JJ pumice) (NN float)) (PP (IN in) (NP (NN water))))) (. .)))