1. Go to Tools ➞ Option ➞ Infrastructure ➞ Product Structure ➞ Nodes Customization.
2. Tick the "Customized display" (if not already ticked) and open the "Configure customized display" window using the "Configure...".
3. In the new window add "Definition" ("#DF") to your product.
4. Close. The CAD Definition should be changed in your CATIA tree.

Note 1: if in the same CATIA session, you visualize another product structure from the PLM, the Definition will appear twice.

Note 2: if you want to keep this setting by default for your future CATIA sessions, you need to save your settings.