Bees in Compost Bin

A couple of weeks ago I turned over the compost in my bin, and after heard what I thought was water running. After I went in doors and put in my hearing aids I realized that this was actually Bees. Many of which were appearing out of the top of the Bin. This morning I had another look and they are still there. I am not intending to empty the bin until possibly next spring. So will have plenty of bees to do there thing in the garden. They appear to be small bumble bees and by the sound loads of them. I dont want to harm the bees but need he compost. Any Idea's.