Not planar tree

There is a twins brother and sister B1 and S1.

And there is another twins brother and sister B2 and S2. And they have been married each other to create two new families B1xS2 and B2xS1.

Each family has a kid, grandchildren, ....

There is a problem to create such a cituation int a tree. I was needed to duplicate brother|sisters. What is correct way to do this?

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