Review the Odoo demo data for Analytic Plans at https://github.com/odoo/odoo/blob/18.0/addons/analytic/data/analytic_account_demo.xml

<record id="analytic_plan_departments" model="account.analytic.plan">
    <field name="name">Departments</field>
    <field name="default_applicability">optional</field>
</record>