Add nodes to a custom node tree I have a custom node tree called MyCustomTreeType. I know that there are scripts to add nodes to the composite and material node trees: Controling compositor by python

How can I use this with my custom tree?
The example of the custom PyNode tree includes information about how to add nodes to the menus via NodeCategory so i'm going to assume you've got menus working. 

(if not: see TextEditor > Templates > Python > Custom Nodes )

If you want to add a node via python, it's the same as with shader trees or compositor trees, except you use data.node_groups.

ng = bpy.data.node_groups['MyNodeTree']
new_node = ng.nodes.new(your_nodes_bl_idname)
new_node.location = (20, 40)