Can I add a product to more than one category at a time?

If you need to assign a product to a few categories (like root, parent categories and sub-categories) , you should disable showing categories as tree. Navigate to System > Configuration > Mass Product Actions > Show Categories as Tree > No:

Magento Mass product Actions - Amasty

 

Now you can indicate the IDs of the categories you need to assign your products to:

 

Magento Mass product Actions - Amasty

 

See more details on Mass Product Actions page
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