A while ago, I came across the JGraphT graph library. Back then, it didn’t support visualization or import of GraphViz‘s dotty format.
However, when I check the library again recently, that had changed. Hence I created a new Weka package, which uses this library to display trees. It also allows exporting the tree in GraphML format.
Here is the link to the new package:
https://github.com/fracpete/jgrapht-treevisualize-weka-package