 Then he ran.
( Then ( he ( ran . ) ) )
(ROOT (S (RB Then) (NP (PRP he)) (VP (VBD ran)) (. .)))
He then started to run.
( He ( then ( ( started ( to run ) ) . ) ) )
(ROOT (S (NP (PRP He)) (ADVP (RB then)) (VP (VBD started) (S (VP (TO to) (VP (VB run))))) (. .)))