Would it be possible to cover it in top soil to make it smooth on top. If it is clay then throw claybreaker over it and that will break it down.You will probably need to use a contact weedkiller to kill off the rough grass. Cover the area with newspaper, three leaves thick at least, and spread fresh chipped bark from a sawmill over it. That will probably stop the weeds long enough to keep it tidy for you. By the time the bark has rotted down the newspaper will also have rotted and you will be able to plant in it.
Christmas trees in pots are designed to last for a short time in a pot then like all conifers they will suffer if not planted in the garden or repotted in a bigger pot.

You could probably cut the rough area with a hover mower, though it wouldn't be easy. Mowing it would eventually cause it to smooth out more, over a number of years. Otherwise, I'd be inclined to dig it over level off and reseed.