On your search view you have something like this:

<filter name="group_employee_id" string="Category" icon="terp-partner" context="{'group_by':'employee_id'}"/>

So, on your action you have to send this by context:

<field name="context">{'search_default_group_employee_id': 1}</field>

What if this treeview is inside a form? Not called from an action.

<tree string="" default_order="field_name">
<field name=""/>
<field name=""/>
</tree>

Should be super simple in all the recent versions of ODOO.

https://youtube.com/shorts/-X-7NHL4dJY

I do this in v7 it require an extension of the widget one2many or many2many

<record id=".............." model="ir.actions.act_window" >

<field name="name">.............</field>

<field name="res_model">.................</field>

<field name="view_type">form</field>

<field name="context">{'group_by':'employee_id'}</field>

<field name="view_mode">tree</field>

<field name="domain">[('active', '=', True)]</field>

</record>

Nice solution