Another answer is "all the sweet flowers in about 8000 acres! You are correct that your honey probably comes from trees. I do not know which ones in your area but in my area, Linden are a big resource. I imagine you have honey locust. Maples also supply nectar in bloom. Hopefully some pro in your area will give you an encyclopedia of your flowering plants. If you know of a commercial beek in your area, look him up and buy him a beer.