Reply to a topic in Discussion board List using CSOM

I am working with a Discussion board list. I need to create the whole list using CSOM from scratch. To which I was able to make the list and topic inside it as folders. But I am not able to add replies to those topics. If I add replies as ListItem it shows as Topic inside the topic.

I wanted to know how to add replies to topics and also how to add replies to replies.