public void put(VersionTag tag, T entry) {
    // Add the version tag to the appropriate map
    VersionSource member = tag.getMemberID();
    TreeMap<VersionTag, T> memberMap = tombstoneMap.get(member);
    if (memberMap == null) {
      memberMap = new TreeMap<>(new VersionTagComparator());
      tombstoneMap.put(member, memberMap);
    }
    T oldValue = memberMap.put(tag, entry);
    Assert.assertTrue(oldValue == null);
  }
Add a new version tag to map
geode-core/src/main/java/org/apache/geode/internal/cache/OrderedTombstoneMap.java