Please find attached a photo of some leaves that are falling from my ornamental cherry tree. There are also dead ones at the end of branches. The tree is very mature and is about 25ft. Many thanks. Mrs Lesley Peacock.
You should do a careful inspection on the bark, branches and leaves of the tree.
Remove any fallen leaves from around the tree and dispose of to help from spreading any disease.
These articles will help you pinpoint the issue.