Sorry for your troubles. That tree does look sad.

Transplant shock is easier to prevent than to cure. There must have been some root damage. Possibly from rough handling, or maybe the roots dried out. I know that doesn't help you right now, but for next time - think of ways you could have done it better.

The best thing you can do now is give it lots of water. I know we usually recommend avoiding over watering, but desperate times call for desperate measures. While it's true that habitual over watering leads to root rot, that particular fungus won't burst forth in just a day of two. So really drench it. No standing water, please, but keep the soil wet.

You may also need to cut off some or all of the leaves. The plant looses water through its leaves (transpiration). When root damage cuts down the uptake of water, reducing water loss can keep it alive. Once it regains its health, new leaves will come.

Some sources also recommend adding a tablespoon of sugar to the water. I can imagine that with the leaves removed there won't be much photosynthesis. Maybe a little sugar can compensate? I don't know if it will help, but it can't hurt.