Right click = Copy / Start this branch on a new tab with this a root - optional keep branch also in origonal
I have used this facility in Microsoft's Visio mindmap templates. You begin to construct a mind map not realizing were you are going to end up. Many branches and sub-branches later you decide this branch is probably better with its own mind map. Now the copy feature was / is great. But this idea would shorten the work in developing of spring mind maps.