Metaballs with Isosurface and Geometry wrapper

Hi guys, 

I`m making a definition trying ti create a metaballs with millipede.

The problem is that I try to generate three branches to assign one diferent Isovalue to each one. The point is that the isosurface can`t work with trees, since it runs with a unique list and it doesn`t create a mesh.So I can´t merge the tree layer of information.

What should i do please!

Thanks very much