Allow multiple output wires from the top of a layer stack

[tschundler]

When duplicating something, it seems to copy the whole tree. Edits to the original do not affect the copy. Most of the time, I suspect that is what users want.

But I was thinking I could use this like Blender geometry nodes and use the original data multiple times. The graph seems to require one input to one output? So there doesn't seem (to me) to be an intuitive way to duplicate geometry - eg transform a shape two different ways and apply a boolean while keeping just one set of original shapes.