code: public static TreeNode<String> parse(final String tree) {
  		return TreeParser.parse(tree, Function.identity());
  	}
docs: Parses a (parentheses) tree string, created with
  {@link Tree#toParenthesesString()}. The tree string might look like this:
  <pre>
  mul(div(cos(1.0), cos(π)), sin(mul(1.0, z)))
  </pre>
  
  @see Tree#toParenthesesString(Function)
  @see Tree#toParenthesesString()
  @see TreeNode#parse(String, Function)
  
  @since 4.3
  
  @param tree the parentheses tree string
  @return the parsed tree
  @throws NullPointerException if the given {@code tree} string is
  {@code null}
  @throws IllegalArgumentException if the given tree string could not be
  parsed