've spent the past 20 minutes looking at your watch 
(ROOT (S (VP (VBP 've) (VP (VBN spent) (NP (DT the) (JJ past) (CD 20) (NNS minutes)) (S (VP (VBG looking) (PP (IN at) (NP (PRP$ your) (NN watch)))))))))
(ROOT (S (VP (VBP ) (VP (VBN ) (NP (DT ) (JJ ) (CD ) (NNS )) (S (VP (VBG ) (PP (IN ) (NP (PRP$ ) (NN )))))))))