PyWBS (Python Work Breakdown Structure) aims to be a simple library for simple dealing with Breakdown Structures. Its core feature is an implementation of a simple tree structure.

As per the definition found on https://www.workbreakdownstructure.com/ :

A work breakdown structure (WBS) is a key project deliverable that organizes the team's work into manageable sections. The Project Management Body of Knowledge (PMBOK) defines the work breakdown structure as a "deliverable oriented hierarchical decomposition of the work to be executed by the project team." The work breakdown structure visually defines the scope into manageable chunks that a project team can understand, as each level of the work breakdown structure provides further definition and detail. Figure 1(below) depicts a sample work breakdown structure with three levels defined.

More info is available on:

https://en.wikipedia.org/wiki/Work_breakdown_structure