I’m going to start going to a traumatic bereavement group this week what should I expect?

I lost my parent to suicide and his death anniversary is coming up this Christmas. I decided it was finally time to try and work things out in any way I could. I looked around my area and found free a traumatic bereavement support group. I’m really anxious and not sure what to expect. I’m worried about the possibility of it making me go into a worse headspace. Can anyone give me a rundown of how it may go? Or any other general advice to prepare myself?