The thing started to grow brighter.
( ( The thing ) ( ( started ( to ( grow brighter ) ) ) . ) )
(ROOT (S (NP (DT The) (NN thing)) (VP (VBD started) (S (VP (TO to) (VP (VB grow) (NP (NN brighter)))))) (. .)))
It started to illuminate more and more.
( It ( ( started ( to ( illuminate ( ( more and ) more ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBD started) (S (VP (TO to) (VP (VB illuminate) (ADVP (RBR more) (CC and) (RBR more)))))) (. .)))