is a copy of a copy of a copy 
(ROOT (S (VP (VBZ is) (NP (NP (DT a) (NN copy)) (PP (IN of) (NP (NP (DT a) (NN copy)) (PP (IN of) (NP (DT a) (NN copy)))))))))
(ROOT (S (VP (VBZ ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (DT ) (NN )))))))))