Then he is very sure. 
( Then ( he ( ( is ( very sure ) ) . ) ) )
(ROOT (S (RB Then) (NP (PRP he)) (VP (VBZ is) (ADJP (RB very) (JJ sure))) (. .)))
He is not at all sure.
( He ( ( ( is not ) ( ( at all ) sure ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBZ is) (RB not) (ADJP (ADVP (IN at) (DT all)) (JJ sure))) (. .)))