1. First, enter editing mode for the Code Tree. This can be done anywhere you can see the Codes Panel.
Doing this will turn the Codes Panel orange.
2. To create a new root code/parent code:
3. To create a new sub-code/child code:
3.1. Float your mouse over the code you wish to add a child code to.
This will pop up a few different buttons to the right of the code as show above.
3.2. Click the 'Add Child Code' button
The pop up will look the exact same as if you were adding a root code.