This is an example of a fungus known as Honey Fungus; it's binomial name is Armillaria mellea
. There are a number of cherry trees around the area in which I live and a good number of them are affected by it. This fungus grows into some of the largest living organisms in the world with one colony in Oregon, USA covering an area of over three square miles... This example presently covers around five square metres, so it has some considerable growing to get to that stage!