purchase_order_unified_menu/views/purchase_view.xml

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

        <record id="action_unified_purchase_order" model="ir.actions.act_window">
            <field name="name">Registro de Compras</field>
            <field name="type">ir.actions.act_window</field>
            <field name="res_model">purchase.order</field>
            <field name="view_type">form</field>
            <field name="view_id" ref="purchase.purchase_order_tree"/>
            <field name="view_mode">tree,form,calendar,graph</field>
            <field name="search_view_id" ref="purchase.view_purchase_order_filter"/>
        </record>

        <menuitem id="menu_unified_purchase_order"
                action="action_unified_purchase_order" parent="purchase.menu_procurement_management"
                sequence="7"/>

    </data>
</openerp>