hi, i am looking for a tree species that is slow growing, an "indoor" or "outdoor" variety will be fine, reacts well to pruning and can usually be found a shohin bonsai in bonsai shops so it can fit in my pot. i've put a water bottle next to the pot in the photos so you get a rough idea of how narrow the rocks are together, also the cement that holds one of the rocks in place is blocking one drainage hole, so the tree has to be quite small or have a small root system.
thanks