…or maybe just nature. What the hell is this?

whaaaa?
It’s some sort of crystal? Fungus? Something. This is the base of a tree in my back yard. The hole is big and I’m concerned the tree is going to crash into my house. What the hell is this thing?
UPDATE: It’s a fungus. It’s not solid like I thought it was. Under direction to “poke it with a stick”, I did just that:

Alien fungus.