I'm new in ODOO and i  write a new sample module and install it on ODOO but it doesn't show on menu can any one help me to solve the problem?

i use ODOO version 12

here is my code:

model.py:

from odoo import models, fields, api

class CustomerModel(models.Model):
    _name = 'customer'

    name = fields.Char(string="Name")
    lastname = fields.Char(string="Last Name")
    age = fields.Integer(string="Age")

customer.xml:

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

<odoo>

        <record model="ir.actions.act_window" id="customers_list_action">
            <field name="name">Customers</field>
            <field name="res_model">customer</field>
            <field name="view_type">form</field>
            <field name="view_mode">tree,form</field>
            <field name="help" type="html">
                <p class="oe_view_nocontent_smiling_face">Create the first Customer
                </p>
            </field>
        </record>

   
        <menuitem id="main_customer_menu" name="Cutomers"/>

        <menuitem id="customer_menu" name="Cutomers"
                  parent="main_customer_menu"/>

        <menuitem id="customers_sub_menu" name="Cutomers" parent="customer_menu"
                  action="customers_list_action"/>


</odoo>