Pyrus and Prunus are very similar when you just have leaves to look at... this one has wavy edges as well as the serrations, which makes me think it could be Callery Pear.
I wouldn't say that 'wavy edges & serrations' is diagnostic of Pyrus over Prunus but agree with Barb that this is a Pear. Pears usually have a leaf that is more circular in shape, many plums have leaves that approach lanceolate. To be frank I tend to eyeball them, it ultimately does not really matter as they are both about as weedy as each other