Branching Project Trees
Only one user can edit an unbranched tree at a time. Branching a tree creates smaller, more manageable sections that enable multiple users to simultaneously edit different branches of the same tree. Only one user, however, can edit a particular branch at a time.
Note: You cannot add a project to a branch from the Project Costing Definition page.
See PeopleTools: PeopleSoft Tree Manager
Tree branches are treated as separate objects in object security. Therefore, you can restrict access to a tree branch. This enables you to secure portions of a tree without creating a separate tree.
See PeopleTools: PeopleSoft Tree Manager