Yes, we had someone last year write in about their Ruan bonsai tree ( https://www.helpfulgardener.com/forum/vi ... an#p334875
) and concluded that Ruan was the brand name/ garden name. That person was in the UK. Are you?
Tom is right ginseng ficus. They are susceptible to dropping leaves when they are moved or conditions change, especially light. But usually those leaves don't turn brown or dry, maybe a bit yellow, but mostly they just fall off. If your leaves are turning brown first, that is probably something else. The good news about dropping leaves easily, is that they also regrow them easily. They are good trees for indoor bonsai, being tropical evergreens.
Those big roots on yours look greenish in the photo. If that is not just a trick of the camera, then something is wrong, should not be like that. Probably is starting to grow algae which is an indication of too much moisture/not enough light. Are you misting your tree? Misting the leaves daily is good for them, but looks like you need to try not to be misting the trunk/exposed roots. I'm guessing your tree is in something like a peat based potting soil. That is not good for bonsai, which need something much more free draining, doesn't hold on to water like peat moss does. Cactus mix will do if you can't find actual bonsai soil. But I wouldn't try repotting it just yet, since you just got it. Best time to do that is spring. But at least let it get settled in, in its new home first.
Here's someone else that just wrote in yesterday to have their ginseng ficus bonsai identified: https://www.helpfulgardener.com/forum/vi ... =1&t=65630
In that thread, I gave some links to more info about bonsai care and some pictures about styles of ginseng ficus bonsai.
Welcome to the Forum!