buy the movie milk when the tv cow is free 
(ROOT (S (VP (VB buy) (NP (DT the) (NN movie) (NN milk)) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NN tv) (NN cow)) (VP (VBZ is) (ADJP (JJ free))))))))
(ROOT (S (VP (VB ) (NP (DT ) (NN ) (NN )) (SBAR (WHADVP (WRB )) (S (NP (DT ) (NN ) (NN )) (VP (VBZ ) (ADJP (JJ ))))))))