The conversation he had overheard had stimulated his curiosity.
( ( ( The conversation ) ( he ( had overheard ) ) ) ( ( had ( stimulated ( his curiosity ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN conversation)) (SBAR (S (NP (PRP he)) (VP (VBD had) (VP (VBN overheard)))))) (VP (VBD had) (VP (VBN stimulated) (NP (PRP$ his) (NN curiosity)))) (. .)))
The conversation made him curious because they spoke about treasure
( ( The conversation ) ( made ( him ( curious ( because ( they ( spoke ( about treasure ) ) ) ) ) ) ) )
(ROOT (S (NP (DT The) (NN conversation)) (VP (VBD made) (SBAR (S (NP (PRP him)) (VP (VBZ curious) (SBAR (IN because) (S (NP (PRP they)) (VP (VBD spoke) (PP (IN about) (NP (NN treasure))))))))))))