```json
{
    "no": ["unknown", "primary", "secondary"], 
    "yes": ["tertiary"]
}
```
The feature "education level" is categorized into four categories: tertiary, secondary, unknown, and primary. When analyzing the relationship between education level and the task, it can be observed that clients with a tertiary education level are more likely to subscribe to a term deposit, whereas clients with unknown, primary, or secondary education levels are less likely to subscribe. Therefore, the clients who subscribed to a term deposit typically have a tertiary education level, while those who did not subscribe can have any education level.