FamilySearch Family Tree (the "Tree" link on the main page) is a single tree with over 1.5 billion people in it. It is intended to have just one record for each person. So in that respect, the comparison to WikiTree is a good one. WikiTree is more restrictive on making changes, etc. The FS Family Tree is a true collaborative tree where anyone can edit any person. With the only restriction being for people who are famous who are locked down and can't be changed.
Actually, if I understand correctly, the underlying structure of the FSFT is actually based on the WikiTree model to a large extent.
The FamilySearch FamilyTree is a single shared tree.