How to implement a custom tree
You can implement a custom tree using code. Learn more about this approach in the article about Section Trees.
You are currently looking at documentation for Umbraco 8 and older versions.
An automated guess is that docs.umbraco.com/umbraco-cms/reference/configuration-for-umbraco-7-and-8/trees/ could be the link to the new documentation for Umbraco 9 and newer versions.
You can implement a custom tree using code. Learn more about this approach in the article about Section Trees.