Q.Problem with a cherry tree
My neighbour’s cherry tree is weeping at the base, and some mof the terminal leaves are sticky. Is this an infection?

This appears to be a sever bacterial canker that most likely will girdle the entire tree; with it sitting at the base of the trunk.
This could be the result of injury at the base of the tree; perhaps a weed trimmer.
Removal of branches that are infected is the best treatment, but this is not possible in this case.
https://www.gardeningknowhow.com/edible/fruits/cherry/bacterial-canker-on-cherries.htm