a film you will never forget -- that you should never forget 
(ROOT (NP (NP (DT a) (NN film)) (SBAR (SBAR (S (NP (PRP you)) (VP (MD will) (ADVP (RB never)) (VP (VB forget))))) (, --) (SBAR (WHNP (IN that)) (S (NP (PRP you)) (VP (MD should) (ADVP (RB never)) (VP (VB forget))))))))
(ROOT (NP (NP (DT ) (NN )) (SBAR (SBAR (S (NP (PRP )) (VP (MD ) (ADVP (RB )) (VP (VB ))))) (, ) (SBAR (WHNP (IN )) (S (NP (PRP )) (VP (MD ) (ADVP (RB )) (VP (VB ))))))))