docs: @Override
    protected void bulkLoad(List<SpatialEntry> spatialObjects) {
      if(!initialized) {
        initialize(spatialObjects.get(0));
      }
      // create leaf nodes
      getFile().setNextPageID(getRootID() + 1);
      List<SpatialEntry> nodes = createBulkLeafNodes(spatialObjects);
      int numNodes = nodes.size();
      if(LOG.isDebugging()) {
        LOG.debugFine("  numLeafNodes = " + numNodes);
      }
  
      // create root
      root = createNewDirectoryNode();
      root.setPageID(getRootID());
      for(SpatialEntry entry : nodes) {
        root.addDirectoryEntry(entry);
      }
      numNodes++;
      setHeight(2);
  
      if(LOG.isDebugging()) {
        StringBuilder msg = new StringBuilder();
        msg.append("  root = ").append(getRoot());
        msg.append("\n  numNodes = ").append(numNodes);
        msg.append("\n  height = ").append(getHeight());
        LOG.debugFine(msg.toString() + "\n");
      }
      doExtraIntegrityChecks();
    }