We will use a simplified version of the res.partner model:

class ResPartner(models.Model): 
    _name = 'res.partner' 
    name = fields.Char('Name', required=True) 
    email = fields.Char('Email') 
    is_company = fields.Boolean('Is a company') 
    parent_id = fields.Many2one('res.partner', 'Related Company') 
    child_ids = fields.One2many('res.partner', 'parent_id', 
                                'Contacts') 
    country_id = fields.Many2one('res.country', 'Country')