Tansadio,

you can not add an attrs attribute like this in tree tag, infact you can keep <tree create="false" edit="false"> and add a new customized button as:

<header>

 <button string="Create" class="oe_button oe_highlight" special="create" name="your_Function" attrs="{'invisible': YOUR_CONDITION}"/>

</header>

and then redirect to form view to create a new record...

Here you can keep your condition also for hiding the button.

Hope it Helps!