I was watching a video by Kishore Gopalakrishna about StarTree Index. In that video, he showed a visualization of the StarTree index for the given data (). Is that tool available for external use?

Yes, the code is here: https://github.com/apache/pinot/blob/master/pinot-tools/src/main/java/org/apache/pinot/tools/StarTreeIndexViewer.java

Thanks @Xiang Fu!