I made a new model to show the sale price based on fixed margin (see code below)
it worked and displayed on the product view normally,

class Corporate(models.Model):
    _inherit = 'product.template'

    Marge = fields.Float(string="Marge")
    Price = fields.Float(string="Price", compute='compute_Price')

    def compute_Price(self):
        self.Price = self.Marge * self.standard_price
        return self.Price

WHen i added the field to product.template tree view, i got this error:

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Program Files\odoo\server\odoo\models.py", line 5119, in ensure_one
    _id, = self._ids
ValueError: too many values to unpack (expected 1)

 File "C:\Program Files\odoo\server\odoo\models.py", line 5122, in ensure_one
    raise ValueError("Expected singleton: %s" % self)
ValueError: Expected singleton: product.template(202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 222, 223, 224, 225, 226, 227, 228, 229, 230, 232, 231, 233, 234, 221, 235, 236, 237, 248, 246, 238, 254, 239, 247, 244, 255, 245)