Q:

Trigger second journey only after completing the first journey

How to trigger journey after completion of another journey. Is it possible ??

A:

In order to do this in real time, you will need to build a custom JB activity, which uses REST API to trigger the next journey. The drawback of this solution, apart from requiring substantial coding, is the fact that your journey 2 will have an API trigger, and hence will not be able to run scheduled or based timed with an automation run. 
You can read about custom JB activities here.
And about triggering journeys with API here.

