its hard to imagine having more fun watching a documentary ... 
(ROOT (NP (PRP$ its) (ADJP (JJ hard)) (S (VP (TO to) (VP (VB imagine) (S (VP (VBG having) (NP (JJR more) (NN fun)) (S (VP (VBG watching) (NP (DT a) (NN documentary))))))))) (. ...)))
(ROOT (NP (PRP$ ) (ADJP (JJ )) (S (VP (TO ) (VP (VB ) (S (VP (VBG ) (NP (JJR ) (NN )) (S (VP (VBG ) (NP (DT ) (NN ))))))))) (. )))