I want to run my form with the 

widget="many2many_tags" in my selection

template.xml : 

<div class="col-md-7 col-sm-8 ">

    <select id="membre_interne" name="x_membre_interne"  class="form-control o_form_input_dropdown" >

      <option value="" >Sélectionnez...</option>

      <t t-foreach="users" t-as="user">

      <option value="" t-att-value="user.login"   >

        <!--- <field name="x_membre_interne" widget="many2many_tags" /> -->
        <t t-esc="user.login"/>

      </option>

      </t>
    </select>
</div>

And in my model.py  my fields is already in many2many : 

x_membre_interne = fields.Many2many("res.users", string="many2many_tags" , readonly=0, website_form_blacklisted=0, Store=True)

Thanks for your help, 

Regards