I am afraid I have no pics... I left them all behind in another country
But I used green moss and big chunks of natural cork, then lichens and tiny plants to complete.
Anyway, I couldn't find a picture that gave the approximate idea either, so here's one of my sad pc drawings to illustrate what I meant, I hope it helps.
Basically, my take is that an uneven surface would look more romantic and compliment the artwork better. So I was thinking of a triangular base. Does it make any sense?
Edit: I'm thinking that then the tree should have an inclination towards the slope, to keep the balance.