What is the intended use of these two things? They seem very similar and I’m wondering if there is some reason to use one or the other. Sometimes it’s good to know what the software authors intended.
You can create a “note” and add content under a node, or you can create a child node and add the same content. In both cases you have some content that you can show or hide, that seems “under” the main node. Obviously if you want more nested expand/collapse, you need the sub-node.