Hi Fasil,

If you want to add chatter in your object, then you will have to inherit the "mail.thread" object in your object as follow:

class MyClass(models.Model):
    _name = 'my.class'
    _inherit = ['mail.thread']

Now, add chatter widget in your form view in XML as follow:

        <record id="view_my_class_form" model="ir.ui.view">
            <field name="name">my.class.form</field>
            <field name="model">my.class</field>
            <field name="arch" type="xml">
                <form>
                    <sheet>
                    .....
                    </sheet>
                </form>
                <!-- Add chatter and followers widget -->
                <div class="oe_chatter">
                    <!-- Followers view -->
                    <field name="message_follower_ids" widget="mail_followers"/>
                    <!-- Chatter view -->
                    <field name="message_ids" widget="mail_thread"/>
                </div>
        </record>