Change Back-Button Form

Hi

I have a navigation view, an after pushing an other view on the root view, there is a back button which is like an arrow.

My question is, is it posible to change the back button form to a normal button without this arrow style?

thank you for your help.

Code:

---

{
  xtype:'navigationview',
  navigationBar:{       
        backButton:{
            ui:'normal'
        }
    }
}

---