I' not a bee expert but they will be of the solitary bee variety, I have them in my garden as they always like my hose reel screw holes every year.
From what I have read they will lay an egg at the end of the tube then block it in and lay another egg etc until the tube is filled. Once the first bee is ready to leave it breaks down the seal and nips the next one to get it to do the same until all the bees are active and leave the tube.
Apologies for a very basic breakdown and it would be interesting to learn what type of bee they are.