account-financial-reporting/mis_builder/report/mis_report_instance_xlsx.xml

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

    <record id="xls_export" model="ir.actions.report.xml">
      <field name="name">MIS report instance XLS report</field>
      <field name="model">mis.report.instance</field>
      <field name="type">ir.actions.report.xml</field>
      <field name="report_name">mis.report.instance.xlsx</field>
      <field name="report_type">xlsx</field>
      <field name="auto" eval="False"/>
    </record>

  </data>
</openerp>