my email templaes like this ：

    <!-- Email template for holiday -->
    <record id="holidays_require_email" model="email.template">
        <field name="name">holiday require</field>
        <field name="model_id" ref="hr_holidays.model_hr_holidays"/>
        <field name="email_from">holiday@test.com</field>
        <field name="email_to">
            <![CDATA[
                % if len(object.employee_id.parent_id):
                  'codefans3@gmail.com '
                % endif
                % for p_id in object.employee_id.parent_id:
                ${p_id.work_email}  
                % endfor
            ]]>
            </field>
        <field name="subject">Holiday require</field>
        <field name="body_html"><![CDATA[

${object.user_id.partner_id.name} have a leave action, please login in opnerp to comfirm

${object.web_url}

but this did not work.
the field parent_id is many2many

how can i do with this

thanks