Is it possible to categorize the existing trips?

Yes, mileage type tracking is a feature that can be added by following these steps:
  1. Access the TMM Store.

  2. Scroll down and click or tap the Add Mileage Type Tracking tile.

  3. When you are ready to purchase, click or tap the Buy button.

  4. Follow the In-App purchase instructions to complete the purchase.

Buying this feature will also allow you to group and sort the existing trips by mileage type.