Five years.
( Five ( years . ) )
(ROOT (NP (CD Five) (NNS years) (. .)))
Its been five years since I have been here.
( ( ( Its ( been ( five years ) ) ) ( since I ) ) ( ( have ( been here ) ) . ) )
(ROOT (S (NP (NP (PRP$ Its) (VBN been) (CD five) (NNS years)) (PP (IN since) (NP (PRP I)))) (VP (VBP have) (VP (VBN been) (ADVP (RB here)))) (. .)))