Well that's the difficulty, every time you have a wedding you are bringing in another tree, and the new spouse will have siblings and cousins that will have the

Well that's the difficulty, every time you have a wedding you are bringing in another tree, and the new spouse will have siblings and cousins that will have their own children and parents. So I think a complete genealogy tree would be impossible to represent in 2d without crossing but most genealogy trees aren't that exhaustive so there must be an algorithm that creates a good representation when it is possible.