Use the 80:20 rule to draw the user's attention to the few subdirectories or files that consume most disk space on that level: Highlight those items, if it makes sense.
Research what approach is most useful to identify such dominant items:
- Average size and standard deviation?
- Median, quartiles and interquartile distance?
- Something else?
Described in great detail here (including screenshots and methodology):
This project is one of its kind!