Oooo, TPP's yellow tree peonies are in flower, but maybe he doesn't want to over do the peony thing (but here and here anyways) . No problem; this time of year lots of things are in flower. At the back of our perennial garden is a spectacular young tree, a Carolina silverbell (Halesia carolina). This is a great ornamental tree, native to SE North America, but completely hardy in Zone 5. They flower when quite young and are tolerant of some shade. TPP has blogged about a different genus in the same family (Styrax americana - American snowbell). You get the idea, dangling white flowers are a thing in this family (Styracaceae - Storax family) and big bees love it. TPP also has a young Pterostyrax tree, but it hasn't flowered yet. Storax makes no sense as a common name because it's a reference to a medicinal resin from the appropriately named Liquidambar styraciflua (sweetgum) (note the specific epithet) which is in another family no matter which one this genus is now in. Seems there was some confusion way back when plant names were based on gum-resins. OK that's not your problem, but this is a highly recommended flowering tree.