Hi - B. cherry is a Eugenia... and is not a 'cherry tree' in the same sense that you're used to. It's a very tropical plant (or possibly subtropical) that likes warm and dry conditions, so while putting it in the ground is theoretically a fast way of growing trunks, unless you're in pan- or S. America, it might not be the best idea. A large(r) pot is probably a good idea, bonsai mix included, and do a little web research into your tree while you're waiting for it to grow up. Maybe start with the "Internet Bonsai Forum" (a lot more going on there than here), and Bonsai4me.com.

I grow a few of Eugenia Myrtifolia- brush cherry. They do thicken up in a pot like ficus do, though they need more water than ficus. Trees will virtually always thicken their trunks faster when in the ground, but the winters cannot be cold for this one.

I've never heard of one that needs more water than Ficus... less often if anything...

I've seen large ficus trees gracing the streets of Haifa, Israel. Pretty dry there. The many species of this tree has a wide range of what it can tolerate. Perhaps were comparing apples to oranges somewhat, but I could clarify to say that EM will not tolerate being as dry as, say, ficus benjamina. Nonetheless, put it in the ground to thicken the trunk if your are in US growing zone 9 or warmer, but if you want to keep it potted it will thicken.