Hi there. Im faily new to Bonsai and trees but to me with that serrated leaves its an Ulmus Parvifolia. Its decidous if u keep outside. It can be inside too that way u make evergreen. I see the leaves are very big. Maybe u could prune back and then next year start with the leaves defoliation thing to reduce size. Do some internet search in Ulmus Parvifolia to see if this is your tree. I have one of those. 5 years old. Im attaching the picture so u can see it. Its about 25 cm height. It like when arrived home. Now I did some pruning and there are no more yellow leaves.
