I won't tell.
( I ( ( ( wo n't ) tell ) . ) )
(ROOT (S (NP (PRP I)) (VP (MD wo) (RB n't) (VP (VB tell))) (. .)))
I'll tell.
( I ( ( 'll tell ) . ) )
(ROOT (S (NP (PRP I)) (VP (MD 'll) (VP (VB tell))) (. .)))