I have planted the tree in a bigger bot and used special bonsai soil. I haven't found any none organic soil yet, I hope this will be good enough for now.
It is an improvement. A remark though... There isn´t such thing as special Bonsai soil. Also, if your whole soil mix is based only in organic material do keep in mind that the watering regime is critical for the thriving (or not) of this tree. Do keep in mind that, in general, organic soils present a poorer drainage than their inorganic counterparts, hence root oxygenation might be impacted as well.
I planted the tree in a bigger bot and hope this will increase the trunk size over the years. I hope this will be better for the tree now.
Be patient... Quite a few years should pass before this tree´s trunk would gain enough girth. Meanwhile do try to keep him alive and enjoy the ride over all things.
Oh... One last thing... Do get rid of that tray... It won´t do no good or it won´t make no difference at all for that matter.
Alain