but it could be , by its art and heart , a necessary one . 
(ROOT (S (CC but) (NP (PRP it)) (VP (MD could) (VP (VB be) (, ,) (PP (IN by) (NP (PRP$ its) (NN art) (CC and) (NN heart))) (, ,) (NP (DT a) (JJ necessary) (NN one)))) (. .)))
(ROOT (S (CC ) (NP (PRP )) (VP (MD ) (VP (VB ) (, ) (PP (IN ) (NP (PRP$ ) (NN ) (CC ) (NN ))) (, ) (NP (DT ) (JJ ) (NN )))) (. )))