Have a look at the following link:
The accepted solution shows how to use import_file to import files in bulk mode.
I am confused.
in the above one, they are talking about completely about stylesheets.
But my requirement is to attach datasets in bulk mode to items.
import_file utility allows you to attach dataset to the item revision. the arguments to be used are: itemRevUid and relationType.
You can specify dataset type using -type argument.