That leaf colour and shape look very much like Leptospermum "Mesmer Eyes" - confim it by comparing at your local native nursery. If it is, it's a very good variety for bonsai - robust, fine detail, coarse bark early, and makes good shapes!
I assume the tag in the pot does not have a name? Looks like a recent acquisistion. No label when you purchased it?
There are so many hybrid Leptospermum and selected cultivars that it is difficult to Id down to cultivar level accurately. You'll need to wait until it has flowers to be more positive on ID other than Leptospermum.
Thank you! Will wait for it to flower to confirm. The label only said 'Tea tree' - it was leftover stock from a nursery that closed, and an opshop has moved into the premises and was selling it and a few other at bargain prices. I got this one, two lilly pillys, and a banksia ericifolia with a 10mm trunk all for $24, all nice and healthy. I've left the banksia, but repotted the others as they looked like they could handle it.