The tree is totally normal, but there was a large branch cut off a long time ago because it was blocking the sidewalk. A small branch is growing out of that cut stump and all those leaves have the left half lobed and the right half toothed. No idea if its a graft, or just natural.
I agree, looks like a mulberry. Leaves on small trees and new branches are particularly likely to be lobed in mulberry, while older branches tend to produce leaves without lobes.