Any various trees such as a Basswood which have nectar-rich flowers attractive to bees.

Here is a link that might be useful: Bee Tree

I believe this is what you are looking for....Evodia danielii. Look at the last bit of information at the very bottom of the right hand column on the link below.

There must be male and female trees, because we have had some that flower, but do not set seed. Maybe someone else can answer that for you. I do know that the bees really work the one that does set seed for us.

Here is a link that might be useful: Korean Evodia

jakeman,
I think you've already got your answers from the previous two postings. A quick 'Google' search makes the connection between Millie's Korean Evodia and the actual term "bee bee tree" as does the more generic use of the term 'bee tree' when referring to trees like the Basswood trees.

There is one point of confusion that really "threw me" for the longest time. While travelling in Europe (Russia), I had the occassion to be offered a light yellowish creamed honey with an unusual (but tasty) flavor. I was told it was honey from the lime tree. Well, I knew lime, right? The green citrus fruit that required a climate much more tropical than this close to the artic circle! My mind was suffering a real "disconnect" here...how is this honey from a lime tree? Must simply be a translation problem...

But this is typical of the problems you run into when the common names of plants are used. A little internet searching upon my return home and before you know it, the discovery was made: Lime tree = Linden tree = Basswood tree.
And the Winter Linden tree (Tilia platyphyllos) is what had provided that wonderful tasting Lime honey! And this honey tasted different from the liquid (extracted) honey from the American Basswood (Tilia americana) so common in your part of the country.

jakeman, I just posted a question about the fertility of the bee bee tree (Korean Evodia) and was told that the name has been changed to Euodia (note! u not v )and Tetradium daniellii. I looked it up as Tetradium daniellii and got lots of hits.