Do you need to be buried in a casket in a cemetery?

Caskets are very expensive. It’s stupid to spend that much money something you’re going to bury. Also, a casket would take a long time to decompose.

When I die, I would liked to be put in a cheap wooden box and be buried by a nice tree. The wooden box would decompose a lot quicker and then I would follow. I would get back to nature much faster and my remains would help give the tree life. Friends and family could come visit my tree.

What are the legal issues that go with burying someone. Does it need to be in cemetery? Does one need to be in a casket?