Due to the recursively defined nature of the behavior tree, the JSON definitions can get messy and unreadable for larger trees. The solution for splitting up different parts of your tree is using a reference to another JSON within your workspace instead of an entire node or tree definition.
Anywhere you could include a node or tree definition, you could instead reference another JSON using the "ref" keyword. The root directory of the tree parser is set to mr_bt/src/tree_jsons/, so your reference provided must be relative to that root directory.
For example, let's say that you are creating a new behavior tree in the folder mr_bt/src/tree_jsons/my_new_tree/ and your folder contains the following:
You want to include move.json and calculate_dist.json as children for a parent node in root.json. This is what that would look like
You can also make references to other behavior tree JSONs as long as they are in the directory mr_bt/src/tree_jsons by providing their path within that directory.