This is my old friend, Monsieur Poirot, whom I have not seen for years."
( This ( ( ( is ( ( ( ( ( my ( old friend ) ) , ) ( Monsieur Poirot ) ) , ) ( whom ( I ( ( have not ) ( seen ( for years ) ) ) ) ) ) ) . ) '' ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (NP (NP (PRP$ my) (JJ old) (NN friend)) (, ,) (NP (NNP Monsieur) (NNP Poirot)) (, ,) (SBAR (WHNP (WP whom)) (S (NP (PRP I)) (VP (VBP have) (RB not) (VP (VBN seen) (PP (IN for) (NP (NNS years))))))))) (. .) ('' '')))
Monsieur Poirot is someone I used to work with back in college. 
( ( Monsieur Poirot ) ( ( is ( someone ( I ( used ( to ( ( work ( with back ) ) ( in college ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Monsieur) (NNP Poirot)) (VP (VBZ is) (NP (NP (NN someone)) (SBAR (S (NP (PRP I)) (VP (VBD used) (S (VP (TO to) (VP (VB work) (PP (IN with) (ADVP (RB back))) (PP (IN in) (NP (NN college))))))))))) (. .)))