How to add an "entry point arrow" to a tab bar controller?

In Xcode 6.2 beta, I am able to make some view controllers such as "View Controller" or "Navigation view controller" the entry point of my interface by dragging and dropping the "entry point arrow" on it, it gives me something like this :
But when I want to drag this arrow on a tab bar controller, it does not work, so is that a bug or should I do it in another way ?

Try with following steps.

1) Open StoryBoard.

2) select TabbarControllerwhich you want to set as RootViewController.

3) Open Properties.

4) select InitialView Controller Option.

For help you can see following image.

its a litile bit confusing over versions on xCode, I'm using version 8.3.2 and it has the follwing

select navigation controller

check the is initial view controller checkbox

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