To me having a stone under a tree represents Buddha in his final meditation when he reaches enlightenment under the tree.
So the stone to me reflects tranquility and peace , but it’s not for everyone.
I found out this is a brush cherry. Exciting new revelation, though it was through someone who posted a sad looking bonsai for $50 in my area when these are only $39 new at the garden Center.
I asked why it was so high , he said because brush cherry is undesirable and his is better quality.