Do not talk.
( ( ( Do not ) talk ) . )
(ROOT (S (VP (VB Do) (RB not) (VP (VB talk))) (. .)))
You should start talking now.
( You ( ( should ( start ( talking now ) ) ) . ) )
(ROOT (S (NP (PRP You)) (VP (MD should) (VP (VB start) (S (VP (VBG talking) (ADVP (RB now)))))) (. .)))