When selecting a category in the Taobao brand application, you can select a primary category and multiple secondary categories. The primary category is the category to which the brand's main products sold on Taobao belong, while the secondary category is the category to which other related products the brand also sells belong.

If you want to apply for the brand of multiple products, you can select the corresponding primary category and secondary category according to the different categories to which these products belong. The specific steps are as follows:

1. Open the Taobao brand application page and select a main category in the "Category" column.

2. In the "Secondary Category" column, you can select multiple secondary categories. If you need to add multiple secondary categories, you can click the "+" sign and then select the required category in the pop-up category selection box. You can repeat this operation to add multiple secondary categories.

3. After selecting all categories to apply for, fill in the brand-related information, upload the brand authorization certificate and other materials, and submit the brand application.

Please note that Taobao has strict requirements for brand applications and requires you to provide sufficient brand certification materials to ensure the legitimacy and authenticity of the brand. At the same time, applicants also need to have certain business qualifications and operational capabilities.