i don't know no i don't
( i ( ( do n't ) ( know ( ( no i ) ( do n't ) ) ) ) )
(ROOT (S (NP (FW i)) (VP (VBP do) (RB n't) (VP (VB know) (SBAR (S (NP (DT no) (FW i)) (VP (VBP do) (RB n't))))))))
I used to know, now I don't.
( ( ( ( ( I ( used ( to know ) ) ) , ) now ) ( I ( do n't ) ) ) . )
(ROOT (S (S (NP (PRP I)) (VP (VBD used) (S (VP (TO to) (VP (VB know)))))) (, ,) (ADVP (RB now)) (S (NP (PRP I)) (VP (VBP do) (RB n't))) (. .)))