Hello Jignasha,

In py :-

 class ProductProduct(models.Model): 
    _inherit = 'product.product' 

    custom_field = fields.Char('Your Field Name',size=50,select=True)

In Xml:-

<record model="ir.ui.view" id="view_product_product_form">
    <field name="name">product.product.form</field> 
    <field name="model">product.product</field> 
    <field name="inherit_id" ref="product.product_normal_form_view"/> 
    <field name="type">form</field> 
    <field name="arch" type="xml"> 
        <field name="name" position="after"> 
            <field name="custom_field"/> 
        </field> 
     </field>
</record> 

demo.xml :-

<?xml version="1.0" encoding="utf-8"?>

<odoo>

<data noupdate="0">

    <record id="hr_department_department_name" model="hr.department">

        <field name="name">Department Name</field>

    </record>

</data>

</odoo>

From this, In Department Name record is created in the department menu.

Hope it works for you.

Thanks,