imagine having more fun watching a documentary 
(ROOT (S (VP (VB imagine) (S (VP (VBG having) (NP (JJR more) (NN fun)) (S (VP (VBG watching) (NP (DT a) (NN documentary)))))))))
(ROOT (S (VP (VB ) (S (VP (VBG ) (NP (JJR ) (NN )) (S (VP (VBG ) (NP (DT ) (NN )))))))))