How to run multiple instances of collection concurrently?

How do I run the “https://github.com/postmanlabs/newman/blob/develop/examples/parallel-collection-runs.js” ?

I don’t have “postman_environment.json” file so I commented that out in the code. When I run the code using command “node parallel-collection-runs.js” I get the following output in console:

undefined
undefined
undefined

I am a newbie in this domain so would appreciate some help.