A closer look at a couple of leaves would be helpful... it's hard to tell with the sun on them (or shadow). Almost looks like a holly, but if you bought it as a 'bonsai' vs at a nursery and then repotted, holly seems less likely. Where are you?

Along with a better pic of the leaves, a picture of the lower trunk would also be helpful. My first thought was Ilex but ficus also came to mind. As moochinka stated the leaf is hard to identify from the current picture