since the thrills pop up frequently 
(ROOT (SBAR (IN since) (S (NP (DT the) (NNS thrills)) (VP (VBP pop) (PRT (RP up)) (ADVP (RB frequently))))))
(ROOT (SBAR (IN ) (S (NP (DT ) (NNS )) (VP (VBP ) (PRT (RP )) (ADVP (RB ))))))