How does the importer build the Category → Subcategory → Item Type tree?

The importer reads the spreadsheet's Category / Subcategory / Item Type columns and finds-or-creates the three-level category tree from them, de-duplicated via an in-memory cache so that even tens of thousands of rows never create duplicate categories. In other words, if a hundred products all sit under Electronics → Phones → Smartphones, the importer creates that path once and links all…

The importer reads the spreadsheet's Category / Subcategory / Item Type columns and finds-or-creates the three-level category tree from them, de-duplicated via an in-memory cache so that even tens of thousands of rows never create duplicate categories. In other words, if a hundred products all sit under Electronics → Phones → Smartphones, the importer creates that path once and links all hundred products to it, rather than spawning duplicate "Phones" categories. The self-referencing category model (each category can have a parent) is what makes the three levels possible, and the importer populates it automatically from the flat spreadsheet columns.