acts_as tree, nested_set, something custom? Which would be best for my situation?

I'm creating a hierarchical tag structure for my portfolio. I have a
few top level tags. those could then have children, those children could
then have children. Pretty standard so far.

Often a child tag will be under more than one parent (i.e. a child might
belong toone or more parents) and it wouldn't necessarily have the same
children under one parent as it would in another.

Do and of the current extensions (acts_as_tree, acts_as_nested_set,
awesome_nested_set, etc) let a child have more than one parent?