A larger pot is one thing (any particular reason?), but it's not ok to plant it deeper than it already is, and/or cover up branches. You'll just end up rotting those parts of the tree that are (newly) under soil. Why would you do that - maybe there are other ways to deal with whatever the problem is.

Lucy's right, what you're suggesting is not a good idea, can lead to rot. Besides, why would you want to do this? What is it you're trying to achieve please?