I know this is answered but I have more to add.
If Honey is slathered on a tree, and is also the last tree that was slathered, there's a 90% chance that it will pick a Pokémon from the same group, so if you already found a Combee on that tree, you will have a larger chance (but not guaranteed) chance of getting another one. Also, the more times a tree shakes, the higher the chance for rare Pokémon. If you have a Ditto (After you get the National Pokédex, you can catch one from the Trophy Garden as a daily Pokémon Mr Backlot talks about, but it's rare. The Ditto are levels 16-18), you can put one with a Combee and keep hatching eggs to guarantee that you get a Combee.