Without having a look at the leaves, it could be one of the very many cultivars of different species.
The bulges at the bottom of the limbs show it was grafted.
Could be a prunus of some sort planted as a street tree for the flowers in spring and the "umbrella" canopy the rest of the year.
Here, there are a few old weeping ash (Fraxinus excelsior 'Pendula') you can see in grdens, they seem to have been very popular at the beginning of the 20th century.