It's definitely grown.
( It ( ( ( 's definitely ) grown ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ 's) (ADVP (RB definitely)) (VP (VBN grown))) (. .)))
It's certainly gotten bigger.
( It ( ( ( 's certainly ) ( gotten bigger ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ 's) (ADVP (RB certainly)) (VP (VBN gotten) (S (ADJP (JJR bigger))))) (. .)))