Well a couple of issues.
1. it was most likely stressed from the transplant. that is usually the #1 reason we see plants suffer post purchase.
2. the gravel, rock, broken pottery in the bottom of the container is probably the single biggest myth for container culture. It actually does the opposite from what all who suggest it are saying. Not your fault I just wish people would stop suggesting it. What happens is all the soil fills in the gaps and now you have raised the perched water column even higher.
3.top soil or dirt should never be used in a container.

your tree might make it if you change the soil but dont do it now. wait to see if it recovers. get that guy into the best sun you can and watch your watering.

Mike

I agree with Mike on all counts, although I would re-pot immediately!

The roots are suffocating or rotten due to the potting mix configuration. It may or may not be able to survive.

Josh