Here is my code :

    <!-- ================================ -->

    <!-- Create a matching from a product -->

    <!-- ================================ -->

    <record model="ir.values" id="product.product_link_to_label">

        <field name="name">Create Matching</field>

        <field name="key2">client_action_multi</field>

        <field name="type">object</field>

        <field name="value" eval="'ir.actions.act_window,' + str(ref('action_create_matching_tree'))" />

        <field name="key">action</field>

        <field name="model">product.product</field>

    </record>

    <record model="ir.ui.view" id="label.tree_new_match">

      <field name="name">Create Matching</field>

      <field name="model">label.label</field>

      <field name="view_type">form</field>

      <field name="view_mode">tree</field>

      <field name="arch" type="xml">

        <tree colors="green:len(products)==0;red:len(products)!=0" default_order='len_products, real_id' create='false' delete='false'>

          <button string="New" type="object" name="new_match"/> <==== THIS Button where i got trouble to pass values trough context

          <field name="nom" string="Name"/>

          <field name="real_id"/>

          <field name="type"/>

          <field name="products"/>

          <field name="len_products" invisible="context.get('len_products')!=1000"/>

        </tree>

      </field>

    </record>     

    <record id="action_create_matching_tree" model="ir.actions.act_window">

        <field name="name">Create Matching</field>

        <field name="res_model">label.label</field>

        <field eval="0" name="sequence"/>

        <field name="view_mode">tree</field>

        <field name="view_id" ref="label.tree_new_match" />

    </record>

Python fun in my label model:
 

def new_match(self):

self = self.with_context(products=self._context.get('active_ids'))

return {

            'name':_("Save a new matching"),

            'view_mode': 'form',

            'view_type': 'form',

            'view_id': False,

            'res_model': 'label.label',

            'res_id': self.id,

            'type': 'ir.actions.act_window',

            'target': 'current',

            'domain': '[]',

'flags': {'initial_mode': 'edit'},

            }