may cause parents a few sleepless hours -- a sign of its effectiveness 
(ROOT (VP (MD may) (VP (VB cause) (NP (NNS parents)) (NP (NP (DT a) (JJ few) (JJ sleepless) (NNS hours)) (, --) (NP (NP (DT a) (NN sign)) (PP (IN of) (NP (PRP$ its) (NN effectiveness))))))))
(ROOT (VP (MD ) (VP (VB ) (NP (NNS )) (NP (NP (DT ) (JJ ) (JJ ) (NNS )) (, ) (NP (NP (DT ) (NN )) (PP (IN ) (NP (PRP$ ) (NN ))))))))