a talking head documentary , but a great one 
(ROOT (NP (NP (DT a) (NML (NN talking) (NN head)) (NN documentary)) (, ,) (CC but) (NP (DT a) (JJ great) (NN one))))
(ROOT (NP (NP (DT ) (NML (NN ) (NN )) (NN )) (, ) (CC ) (NP (DT ) (JJ ) (NN ))))