Knowledge base is a common documentation layout, without topic tree, or should we say, 2-level tree. There is no topic hierarchy, topics are grouped into "Categories". The main page has links to all topics. It looks like this:
To generate a Knowledge Base from an existing project you need to add "kbdefault" template to the project first.
There's a post on our blog that covers in more detail creation of knowledge bases with Helpinator: https://www.helpinator.com/blog/2019/09/20/how-to-create-a-knowledge-base-with-step-by-step-guides/