It is quite common to see bees in a tree-especially oak trees. The void can be so large that the bees can have a full hive with 100,000 bees within it. Killing the bees in this situation is just a band aid. The best way is to trap the bees which removes the honey and bees. Of course trapping is very time consuming and can take 6-8 weeks if done properly. Don’t listen to those bee removalists that say they can do it in 3 weeks. If you hear less than 6 weeks, then they absolutely have no idea what they are doing.