trial fee

You should review the written retainer contract with your lawyer, it probably was a flat fee which included plea or trial.  I assume that at some point you entered a plea rather than going to trial. The decision to plead rather than go to trial is based upon the advice of your lawyer, which is what you paid for.  A lawyer will file a notice of appearance, request and review discovery from the state, obtain and review the dui video, and enter into negotiations with the state attorney and attend several court hearings before advising you of whether to go to trial or not. It is quite possible that the lawyer decided that you would have a losing case and if you went to trial you may have faced a jail sentence instead of probation as part of a plea. In many cases you are paying for the reputation and experience of the lawyer and some lawyers collect a flat fee which includes a trial.