I have an oak tree with really sticky leaves....

I wouldn't suggest using any kind of pesticide or treatment on an oak tree - this tree supports more forms of life than any other in Britain, and it would be a shame to destroy that. I don't know where you live, but in the South, we've had no rain to speak of - that's what's making you notice this problem more - if we'd had rain on and off, it would wash off the sticky.
The only thing I would say is, are you sure they ARE bees and not wasps or hornets, both of which may have made a nest in the tree, in particular hornets? If you have a wasp or hornet nest, it should be removed by a professional.

I agree with Bamboo about the oak trees wildlife support - but please, please don't destroy hornet's nests - they are even more scarce than bees and contrary to popular belief they are not going to chase you and sting you to bits, they are not interested in us!!