A categoryTreeId is a unique eBay-assigned ID value that represents the root node of an eBay category tree. A category tree is a hierarchical framework of eBay categories that begins at the root node of the tree and extends to include all the child nodes in the tree. Each child node in the tree is an eBay category, and each is represented by a unique categoryId value. Within a category tree, the leaf nodes are the nodes that have no child nodes. The root node of a category tree is often used to define the default category tree used by one or more eBay marketplaces.
See the Field Index to learn which calls use categoryTreeId.