spend years trying to comprehend it 
(ROOT (VP (VB spend) (NP (NNS years)) (S (VP (VBG trying) (S (VP (TO to) (VP (VB comprehend) (NP (PRP it)))))))))
(ROOT (VP (VB ) (NP (NNS )) (S (VP (VBG ) (S (VP (TO ) (VP (VB ) (NP (PRP )))))))))