comes along only occasionally , one so unconventional , 
(ROOT (S (VP (VBZ comes) (ADVP (RB along)) (ADVP (RB only) (RB occasionally)) (, ,) (NP (NP (CD one)) (ADJP (RB so) (JJ unconventional)))) (, ,)))
(ROOT (S (VP (VBZ ) (ADVP (RB )) (ADVP (RB ) (RB )) (, ) (NP (NP (CD )) (ADJP (RB ) (JJ )))) (, )))