Sure, this is how many professional tree growers in our whereabouts grow trees. Uppotting every few months, when a stable rootbal has formed. Use good quality commercial growing soil. Never compact soil.
I see.. I've already done the moving to the 2 gallon pots, and I also added a tile under the already formed roots so they can spread out nicely to later form some nice nebari on some of the trees.
And I use a mix of organic mulch and basic garden soil.. I was just asking if i should compact the top soil so the tree remains held in place without any wires.