This forum is for yEd questions only. The decision tree you linked to was not created with yEd. Rather it is a showcase application demonstrating the capabilities of the yFiles diagramming library. yFiles is not intended for end users but for software developers that create their own applications. If you are a software developer, please visit the yFiles linked above, decide on a programming platform, and request an evaluation version of the appropriate yFiles bundle. (Evaluation version may be requested from the platform-specific yFiles sites.)
