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
Try with following steps.
1) Open StoryBoard.
StoryBoard
2) select TabbarControllerwhich you want to set as RootViewController.
TabbarController
RootViewController
3) Open Properties.
Properties
4) select InitialView Controller Option.
InitialView Controller
For help you can see following image.
image