docs: protected void insertDirectoryEntry(E entry, int depth) {
      lastInsertedEntry = entry;
      // choose node for insertion of o
      IndexTreePath<E> subtree = choosePath(getRootPath(), entry, depth, 1);
      if(getLogger().isDebugging()) {
        getLogger().debugFine("subtree " + subtree);
      }
  
      N parent = getNode(subtree.getEntry());
      parent.addDirectoryEntry(entry);
      writeNode(parent);
  
      // adjust the tree from subtree to root
      adjustTree(subtree);
    }