'I don't know what happened, exactly.' I said.
( ' ( ( ( ( ( I ( ( do n't ) ( know ( what ( ( happened , ) exactly ) ) ) ) ) . ) ' ) ( I said ) ) . ) )
(ROOT (S ('' ') (S (NP (PRP I)) (VP (VBP do) (RB n't) (VP (VB know) (SBAR (WHNP (WP what)) (S (VP (VBD happened) (, ,) (ADVP (RB exactly)))))))) (. .) ('' ') (S (NP (PRP I)) (VP (VBD said))) (. .)))
I knew what had happened.
( I ( ( knew ( what ( had happened ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBD knew) (SBAR (WHNP (WP what)) (S (VP (VBD had) (VP (VBN happened)))))) (. .)))