When a queen bee breaks away from a colony, she will take with her a swarm of worker bees with her. When she rests, these workers will surround her in a cluster to protect her while she is resting. They can stay in this area for up to 3-4 days and then move on to re-colonise.
This is normally unfortunately when they land in the wrong area such as trees in schools, by hospital entrances, where there is plenty of public foot traffic, etc., and they have to be either moved on physically or eradicated onsite. Wherever possible, we move the bees on or get a bee company to remove them – eradication is always a last resort and has to happen in certain circumstances, such as when they are not just resting, but instead nesting inside within structures.