Time, Cost and Scope management tree structuresare defined with 3D WBS method.
3D WBS method goes further of project structuration, I call it then 3D Project Management. It is 3D structured projects with advanced project management methods.
Then, it must be understood that Time, Cost, and Scope variations are managed in the same way. There are always a baseline and a current state that are compared periodically. The result of this comparison is the variation.
Variations shall be managed as qualitative risks. It shall be identify, classify, prioritized, treated, and capitalized.
Variations shall be classified, managed, and traced as shown on the figure below.
Variation sheets can be done to formalize the variations.