by choice

Từ điển WordNet v3.1 - WordNet Dictionary

adverb

with intention;
in an intentional manner
- he used that word intentionally
- I did this by choice
• Syn:
intentionally, deliberately, designedly, on purpose, purposely,
advisedly, by design
• Ant:
accidentally (for: deliberately), unintentionally (for: intentionally)
• Derived from adjective:
deliberate (for: deliberately), intentional (for: intentionally)