Native to the eastern United States, the common buttonbush (Cephalanthus occidentalis) attracts both birds and butterflies with its inch-wide, white spherical blossoms.
Buttonbush is a shrub in the Rubiaceae family, often used as an ornamental plant or windbreak. It can get to be pretty large, about 8′ high and 14′ wide.
(I am NOT a plant person. Here is a much better exploration of the button bush, by Bee Culture Magazine.)