The most common and most likely answer to this crossword clue is the 10 letter word PERQUISITE
I've seen this crossword clue in The Times
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More clues leading to the result PERQUISITE
Buddy explains!

The straight part
We know that "a bonus" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a bonus = perquisite.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PERQUISITE mean?
PERQUISITE noun- (chiefly in the plural) Any monetary or other incidental benefit beyond salary.
- A gratuity.
- A privilege or possession held or claimed exclusively by a certain person, group or class.