a riddle wrapped in a mystery inside an enigma 
(ROOT (NP (NP (DT a) (NN riddle)) (VP (VBN wrapped) (PP (IN in) (NP (DT a) (NN mystery))) (PP (IN inside) (NP (DT an) (NN enigma))))))
(ROOT (NP (NP (DT ) (NN )) (VP (VBN ) (PP (IN ) (NP (DT ) (NN ))) (PP (IN ) (NP (DT ) (NN ))))))