Thank you for your message. The insect in your photo is called the grapevine beetle. Here is our online article. https://hortnews.extension.iastate.edu/2008/7-30/grapevinebeetle.html The larvae of this large beetle live in wet, rotted wood. They could have lived in the decayed tree roots but the hole when they emerged would be 1 inch in diameter at most. Larger holes could be dug be raccoons or skunks trying to reach the grubs in the roots. Thanks. Donald Lewis