NVivo recommends following the catalogue system of coding which uses hierarchies. Please watch Principles of Coding before you embark on your own project
Creating hierarchies allows you to better organise your codes. This is particularly useful if you have a lot of codes that can be grouped into themes. In our example, we have a number of codes that represent positive and negative feedback. We will organise our codes into these two themes by creating parent codes. Codes assigned to a parent code are called child codes. Let’s create two parent codes: Positive Feedback, and Negative Feedback.

Note: the number of files, and references are zero for the parent codes. To rectify this:
Note: your numbers may be different than seen here depending upon how you coded. What is important is that the child numbers add up to the parent number:

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