and the mighty Google said:
The ePub eBooks Metadata Mess!
Basically you will need a Software called Calibre to set the metadata on eBooks to be able to sort them by category.
Yes, it is FREE !
Here is a SAMPLE.
Next step:
Getting eBooks from Calibre to Your Device Using Send to Device and the Connect/Share Functions.
A special plugboard that you may want to create is a “genre” plugboard that corresponds with a “genre” or “tag” field.
Using this in conjunction with iBooks can sort your books into separate categories on your iOS device.
First, create a custom field that you will want to use to sort your iBooks. You may generically name it “genre” in case you want to use it for some other purpose otherwise you could name it “ibooks_cat” or something like that. For column type, select “Text, column show in the tag browser.” As with any new column, you will have to restart calibre. Go through and mark the books in your library. Alternatively, you can use the existing “tag” field. Then create a new plugboard: Format=epub | Device=apple | Source template {#usercolumn} or {tags} | Destination field=tags. Save and then “Apply”.