I had rejected it as absurd, nevertheless it persisted. 
( ( ( ( ( I ( had ( rejected ( it ( as absurd ) ) ) ) ) , ) nevertheless ) ( it persisted ) ) . )
(ROOT (S (S (NP (PRP I)) (VP (VBD had) (VP (VBN rejected) (S (NP (PRP it)) (ADJP (RB as) (JJ absurd)))))) (, ,) (ADVP (RB nevertheless)) (S (NP (PRP it)) (VP (VBD persisted))) (. .)))
It persisted even after I rejected it as an absurdity.
( It ( ( persisted ( even ( after ( I ( ( rejected it ) ( as ( an absurdity ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBD persisted) (SBAR (RB even) (IN after) (S (NP (PRP I)) (VP (VBD rejected) (NP (PRP it)) (PP (IN as) (NP (DT an) (NN absurdity))))))) (. .)))