Oh shoot, everyone else is playing...my guess is Ulmus americana. Dirr's Manual of Woody Landscape Plants notes 3 distinct habits which include "a vase-shaped form in which the trunk divides into several erect limbs strongly arched above and terminating in numerous slender, often pendulous branchlets.
Also has the oblique leaf base and double serrated leaves w/ pointed tip and leaf veins running straight to margin.
