Hello,

You can put one more button "Create and Copy" which call create method and after calling create method it calls copy method.

or you can refer this module which copy records from selected records in wizard and customise for your model.

https://apps.odoo.com/apps/modules/10.0/tko_base_multiple_duplicate/

Also see this  which creates records on onchange:

https://www.odoo.com/forum/help-1/question/onchange-event-of-o2m-and-m2m-4081

Thanks