well in order to achieve this , i had to create a main action wich regroup two actions for the new views :

<record id="action_1" model="ir.actions.act_window">
   <field name="name">new view</field>                                         
   <field name="res_model">model.name</field>                                  
   <field name="view_type">form</field>                                        
   <field name="view_mode">tree,form</field>                                   
   <field eval="False" name="view_id"/>                                        
</record>

so this is the main action , now we should create actions for each view: action 1 for our new tree view

<record id="action_new_tree" model="ir.actions.act_window.view">     
    <field eval="1" name="sequence"/>  
    <field name="view_mode">tree</field>  
    <field name="view_id" ref="external id of your new tree view"/>
    <field name="act_window_id" ref="action_1"/>
</record>

now we made an action for our new tree view , and link it the first action ,we should do the same for the form

<record id="action_new_form" model="ir.actions.act_window.view">     
    <field eval="1" name="sequence"/>  
    <field name="view_mode">form</field>  
    <field name="view_id" ref="external id of your new form view"/>
    <field name="act_window_id" ref="action_1"/>
</record>

perfect , all we need now is to create a menuitem for the first action (action1)

<menuitem id="id_of_ur_new_menu"  
 name="new form and tree view for an existing model"               
 parent="parent.menu "               
 action="action_1"/>