Come in, please! 
( ( Come in ) ( , ( please ! ) ) )
(ROOT (S (PP (VBN Come) (PP (IN in))) (, ,) (VP (VB please)) (. !)))
Don't come in! 
( ( ( Do n't ) ( come in ) ) ! )
(ROOT (S (VP (VB Do) (RB n't) (VP (VB come) (PRT (RP in)))) (. !)))