 Yes, I understand.
( Yes ( , ( I ( understand . ) ) ) )
(ROOT (S (INTJ (UH Yes)) (, ,) (NP (PRP I)) (VP (VBP understand)) (. .)))
I understand that.
( I ( ( understand that ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBP understand) (NP (DT that))) (. .)))