Do remember that Wikitree functions as a single, collaborative family tree, there is no such thing as "your tree" and "my tree".
If you've found an lready exisiting profile for part of the tree that you are working on, you can link that profile to the line you are working on and then continue from there.
Make sure to not create duplicated profiles for the same individuals, and if you do happen to, me sure to initiate a merge.