There are two many2one fields. From these two fields
(assigned_to.assigned_quantity & vendor_name.unit), 
I want to calculate the difference between them. Please check the below code.

@api.depends("assigned_to.assigned_quantity", "vendor_name.unit")
    	​def _compute_quantity(self):
        		​​total_buy = 0
        	​	​total_assign = 0
        	​	​for record in self:
            	​	​	​for rec1 in record.assigned_to:
                    		​	​	​​total_assign += rec1.assigned_quantity​
            	​	​	​for rec2 in record.vendor_name:
                    	​	​	​	​total_buy += rec2.unit
            	​	​	​quantity = total_buy - total_assign
            	​	​	​record.quantity_new = quantity

The code is showing proper value in the form view.

Though when I use it tree view it shows cumulative value. 

Is there any way to fix it? 

Thank you.