'll know a star when you see one . 
(ROOT (S (VP (MD 'll) (VP (VB know) (NP (DT a) (NN star)) (SBAR (WHADVP (WRB when)) (S (NP (PRP you)) (VP (VBP see) (NP (CD one))))))) (. .)))
(ROOT (S (VP (MD ) (VP (VB ) (NP (DT ) (NN )) (SBAR (WHADVP (WRB )) (S (NP (PRP )) (VP (VBP ) (NP (CD ))))))) (. )))