Please have a look at the example in the release blog: https://www.mendix.com/blog/release-9-6-makes-your-mendix-world-spin/
The example in the release blog is fine to get a basic idea of what the Tree Node widget does but it is not a working demo project that shows how to build a more complex use case. For example, the docs say to nest Tree Node widgets but there is no help on how to do that, how do the nested Tree Nodes reference the data in the higher level Tree Nodes?
How about a data hierarchy based on an entity with an association back to itself?
The original question asked about actions, can you create a button to expand or collapse all of the nodes?