What is causing my cherry tree to look like the base of the trunk is rotting away.?
Certified GKH Gardening Expert
It appears your tree is suffering from an advanced case of Phytophthora; crown and root rot.
This is a fungal infection that attacks the roots of the Cherry Tree.
This link has more information.
Treating these diseases can prove difficult and can sometimes requires multiple applications of fungicidal or anti-bacterial sprays.