docs: TreeString split(final String prefix) {
          assert getLabel().startsWith(prefix);
          char[] suffix = new char[label.length - prefix.length()];
          System.arraycopy(label, prefix.length(), suffix, 0, suffix.length);
  
          TreeString middle = new TreeString(parent, prefix);
          label = suffix;
          parent = middle;
  
          return middle;
      }