Q: There is a fungus growing on our old oak tree. It stands only about 20 feet from our two story ranch and is about two and one half times the height of the house.
A: The tree was likely there before the house was built. At some point, soil was pushed up around the base of your oak. Excess moisture led to an invasion of wood rot inside the trunk, which the mushrooms now signify.
Sadly, in my opinion, the tree needs to be removed. Once rot has invaded a tree trunk it can not be cured.