it is hard to tell who is chasing who or why 
(ROOT (S (NP (NP (PRP it))) (VP (VBZ is) (ADJP (JJ hard)) (S (VP (TO to) (VP (VB tell) (SBAR (SBAR (WHNP (WP who)) (S (VP (VBZ is) (VP (VBG chasing) (NP (WP who)))))) (CC or) (WHADVP (WRB why)))))))))
(ROOT (S (NP (NP (PRP ))) (VP (VBZ ) (ADJP (JJ )) (S (VP (TO ) (VP (VB ) (SBAR (SBAR (WHNP (WP )) (S (VP (VBZ ) (VP (VBG ) (NP (WP )))))) (CC ) (WHADVP (WRB )))))))))