<xpath expr="//tree" position="attributes">
 <attribute name="decoration-danger">product_id ==</attribute>
</xpath>

In Odoo 12, I would like to pass a value of a certain product id, that i have defined in data.xml and i would like to use self.env.ref('my_module.my_product_id).id  for this equation. This way the order line product would stand out with a red color, the code works if i go for 'product_id == 420' but i cant use a function? Any idea for this solution? Thank you