I'm able to create a button when select multiple record by adding this header tag in tree view
<tree create="false" delete="false">
<header>
<button name="action_cancel" type="object" string="Cancel" class="btn-danger"/>
</header>
...
...
</tree>
As you can see, there is no space button 8 selected button and cancel button. How can I add a space for that buttons?