Category trees are hierarchical sets of product categories. Unlike product schemas/taxonomies, products can be assigned to any number of categories across any number of category trees.
A product can be categorised in many different ways depending on the application. For example, a laptop product might be categorised in a printed catalogue as: Computing > Portable > Laptop, but on a promotional website as Back to School > Notebooks, and in UNSPSC as Information Technology Broadcasting & Telecommunications > Computer Equipment & Accessories > Computers > Notebook Computers.
Category trees in Pimberly allow you to build and manage these alternate hierarchies and the products within them, and can also be directly associated with particular Channels.