code: public final ParseTree parseTree(CharSequence source) {
      ScannerState state = new ScannerState(source);
      state.enableTrace("root");
      state.run(this.followedBy(Parsers.EOF));
      return state.buildParseTree();
    }
docs: Parses {@code source} and returns a {@link ParseTree} corresponding to the syntactical
  structure of the input. Only {@link #label labeled} parser nodes are represented in the parse
  tree.
  
  <p>If parsing failed, {@link ParserException#getParseTree()} can be inspected for the parse
  tree at error location.
  
  @since 2.3