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 very sure because someone told him.
( He ( ( ( is ( very sure ) ) ( because ( someone ( told him ) ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBZ is) (ADJP (RB very) (JJ sure)) (SBAR (IN because) (S (NP (NN someone)) (VP (VBD told) (NP (PRP him)))))) (. .)))