const RootStack = StackNavigator({
  RootTab: { screen: RootTab },
  RootTwo: { screen: RootTwo },
});
const RootTab = TabNavigator({
  ChildStack: { screen: ChildStack }
});
const ChildStack = StackNavigator({
  UserScreen: { screen: UserScreen }
});

const RootStack = StackNavigator({
  RootTab: { screen: WrapperRootTab },
  RootTwo: { screen: RootTwo },
});
const RootTab = TabNavigator({
  ChildStack: { screen: ChildStack }
});
class WrapperRootTab extends React.Component{
  render(){return <RootTab/>}
}
const ChildStack = StackNavigator({
  UserScreen: { screen: UserScreen }
});