Copying my Mac Photos library to my iPad Photos library

I have an older iPad which is unable to get updates any longer. I was thinking about removing as many programs and stored data as possible and then using it primarily as a Photos viewer. I have all of my photos stored and organized into folders in Photos on my Mac. How would I go about copying my Mac's Photos library to my iPad's Photos library , while still maintaining my Mac's Photos folder structure? I do not use iCloud, as my photo collection is too large to be affordable storage on iCloud. I assume that I would have to transfer via the USB cable from my Mac to my iPad. Exactly how could I do this?