Should I disclose cheating incident if I am not asked?
Why complicate your life? Hopefully you have learned from your errors and moved on. I see no reason to bring it up, but would be careful to reply honestly to any questions that actually do arise. 

Many students have some transgressions in their past. Many are never called to account. Most, we hope, overcome the need and tendency to cheat and develop better life skills. 

I think that if you were intending to repeat bad behavior in the future then you wouldn't be asking a question like this. The application materials for graduate study never, to my knowledge, ask you why you should not be admitted.