What does the cryptic crossword clue "Extract of 'Chicago', live rehearsal for musical (6)" mean?

The definition is "musical". The wordplay uses a hidden word. Hidden in "extract of 'chicagO', LIVE Rehearsal for musical" The answer is Oliver.

Extract of 'Chicago', live rehearsal for musical (6)

Telegraph Prize Cryptic #3002 | 21 Down | 2019-05-05 flower