I’m just using recycled akadama, pumice, lava. I may have added some fit bark fines as well. The container it was in before has a mesh bottom, so the vigorous growth is mostly attributable to the volume of soil in the oversize container and to letting roots escape through the mesh bottom when I had it sitting on a raised bed planter. You could probably get more growth by using more organics in the mix, with the caveat that you’d need to pay more attention to watering so you don’t drown it.
When I repot my trees, I save the old soil and spread it out in one of those big plastic trays they sell at Home Depot and Lowe’s (they’re made for mixing concrete). I leave the tray in the garage for a season to dry out. I then sift it to get rid of the dust and grade it into batches of uniform particle size. When I repot trees in development, I use the recycled soil.