Hello Samba,

You have to add a custom web code for the individual button same as 'Create' in 'tree' view.

The altenate is that you can add a button(wizard) to 'More' menu and from that you can pop-up a window(wizrad) and add a button type object over there and can get the 'active_ids' through 'context' in your method.

To add a button(wizard) in 'More' option, you have to create "act_window" of your wizard like this:

https://github.com/odoo/odoo/blob/master/addons/stock/wizard/stock_return_picking_view.xml#L4

Thanks.