I'm a licensed beekeeper in addition to being an arborist. The bees are just there to gather nectar and pollen from the flowers on the tree. In a month when the flowers are gone, the bees will be too. Bees only sting when trying to defend their colony, comb and brood and unless they've colonized your tree, none of those items are present there. They're just grocery sh0pping in your tree, so you don't need to worry about them. It's actually a good opportunity to get under the tree and enjoy the sound of their contented hum as they gather pollen and nectar to take back to their colony.