Years ago I rescued a tiny christmas tree which had been left in a sack dumped by the plantation planters (sounds like it was a kitten
) I was being self-righteous and clearing up their litter and noticed this one tree abandoned and alone. I planted it in my hedge and for a couple of years it didn't do well and I thought it must have been left dry for too long. However, it's now much taller than me and growing strongly, not as tall as its chums a couple of fields away, but happy and healthy
Trees don't like pots much, so if there is somewhere you can put it in the ground it will prefer that.