That is well. 
( That ( ( is well ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ is) (ADVP (RB well))) (. .)))
That is very well, but I don't know.
( ( ( ( ( That ( is ( very well ) ) ) , ) but ) ( I ( ( do n't ) know ) ) ) . )
(ROOT (S (S (NP (DT That)) (VP (VBZ is) (ADJP (RB very) (JJ well)))) (, ,) (CC but) (S (NP (PRP I)) (VP (VBP do) (RB n't) (VP (VB know)))) (. .)))