Yours is a good question and probably one that a lot of new contributors at Wiki
Tree share. As with most technical details or problems, I will suggest you try the 'Help' area in the top right of each web page and go to the index. For this question I would recommend starting at: http://www.wikitree.com/wiki/Multiple_Parents
Please keep in mind that on any page of the WikiTree, if something is in green you can click on it to take you where you want to go...