This may be a Manchurian pear - pyrus ussuriensis, but apart from the shape I am not sure how to distinguish it from pyrus calleryana. The flowers had a distinct slightly pungent aroma.
The leaf of Manchurian Pear tends to be finely serrated, while that of the Caley Pear is more bluntly serrated. The cultivars of Caley Pear are self infertile, unfortunately the increasingly popular use of multiple varieties enables cross fertilisation and viable seed in pea-sized fruit that birds is spreading into our bush.