Yes, bees love trees especially if their flowers produce nectar, such as willow, maple, plum, cherry, apple, buckthorn, hawthorn, black locust, tulip poplar, basswood and etc. Pollens from non-nectar producing trees are not popular with my bees (I regularly look at bee-pollen under microscope), except hazelnut in mid-late winter here (Zone 8). But I did find some oak, pine (or spruce), and true cedar, so I guess it depends what else is available at the time.