docs: private IntIterator getCommonSplitDimensions(N node) {
      Collection<SplitHistory> splitHistories = new ArrayList<>(node.getNumEntries());
      for(int i = 0; i < node.getNumEntries(); i++) {
        SpatialEntry entry = node.getEntry(i);
        if(!(entry instanceof XTreeDirectoryEntry)) {
          throw new RuntimeException("Wrong entry type to derive split dimension from: " + entry.getClass().getName());
        }
        splitHistories.add(((XTreeDirectoryEntry) entry).getSplitHistory());
      }
      return SplitHistory.getCommonDimensions(splitHistories);
    }