Tree leaves have black fungus.
What you're seeing is called sooty mold. This fungal mold grows in the sugary excrement (known as honeydew) of a type of insect called scale. The scale insect looks like a small bump and is usually on the bark or the underside of the leaves above the sooty mold.
There are many types of scale insects that infest different types of trees and shrubs. In order to help you, we need to know what kind of tree or shrub you have (or give us a clear photo of the leaves/flowers/berries, etc.) Also, if you can see the scale, what does it look like? Or send us a photo of that.
We'd also recommend that you read through this basic information on scale insects to understand your options: