You ask your dad if he rooted a cutting or if he grafted it. Then we can answer your question better.

A cutting, not a graft

Then leave the tree alone for another month. If the main trunk resprouts branches remove the ones down low. If it doesn't pick one growing from the roots to be the new main trunk and remove the rest including the dead trunk.

Pics?

I will take pictures tomorrow. it is thunderstorming outside at the moment. I was outside doing a little yard work when the storm came up, suddenly I might add.