If I had chosen to be an actor, I should have been the greatest actor living! 
( ( If ( I ( had ( chosen ( to ( be ( an actor ) ) ) ) ) ) ) ( , ( I ( ( should ( have ( been ( the ( greatest ( actor living ) ) ) ) ) ) ! ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (PRP I)) (VP (VBD had) (VP (VBN chosen) (S (VP (TO to) (VP (VB be) (NP (DT an) (NN actor))))))))) (, ,) (NP (PRP I)) (VP (MD should) (VP (VB have) (VP (VBN been) (NP (DT the) (JJS greatest) (NN actor) (NN living))))) (. !)))
I did not choose to become an actor, as at the time I lacked the confidence to make that first step. 
( I ( ( ( did not ) ( ( ( choose ( to ( become ( an actor ) ) ) ) , ) ( as ( ( at ( the time ) ) ( I ( lacked ( the ( confidence ( to ( make ( that ( first step ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP I)) (VP (VBD did) (RB not) (VP (VB choose) (S (VP (TO to) (VP (VB become) (NP (DT an) (NN actor))))) (, ,) (SBAR (IN as) (S (PP (IN at) (NP (DT the) (NN time))) (NP (PRP I)) (VP (VBD lacked) (NP (DT the) (NN confidence) (S (VP (TO to) (VP (VB make) (NP (DT that) (JJ first) (NN step))))))))))) (. .)))