DDE provides a Nature Creator for you to add or remove BTT nature file.
After adding BTT nature to your project, your project is tagged as a BTT project. The btt.xml file is recognized as the nature file, which is the effective central controller for the project. Then other BTT tools can access the configuration items and values in the nature file. The configuration in the btt.xml is used across the entire project. You can also remove the BTT nature.
Click Finish, the selected btt.xml file becomes the BTT nature file. Then your project becomes a BTT project as shown in the following screen capture: