For a university project, I needed an Interval Tree data structure, and what's out there was not satisfying, so I built my own. It supports insertion, deletion and queries, supports multiple entries per interval, is not static and not concurrency-safe.
For a simple usage example, have a look at the de.tinloaf.intervaltree.test package. You can also have a look at the api documentation at [https://tinloaf.de/~tinloaf/software/intervaltree/doc/].