I nodded again.
( I ( ( nodded again ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBD nodded) (ADVP (RB again))) (. .)))
I nodded twice in order to acknowledge I understood.
( I ( ( ( nodded twice ) ( ( in order ) ( to ( acknowledge ( I understood ) ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBD nodded) (ADVP (RB twice)) (SBAR (IN in) (NN order) (S (VP (TO to) (VP (VB acknowledge) (S (NP (PRP I)) (VP (VBN understood)))))))) (. .)))