Like Frank said, there's that option and there's also the "restrict to underlying object", which is not available for the global ecopainter but it's available for the normal ecosystems' painter (you didn't mention which eco you're talking about). The two options are similar but not the same.

There's another possibility: just put the tree in a layer of its own and hide the layer. This could be useful if you want to see well what you're doing.