How to use the lark.tree.SlottedTree function in lark

def __init__(self):
        terminals = [TerminalDef(name, PatternRE(value)) for name, value in TERMINALS.items()]

        rules = [options_from_rule(name, x) for name, x in  RULES.items()]
        rules = [Rule(NonTerminal(r), symbols_from_strcase(x.split()), i, None, o) for r, xs, o in rules for i, x in enumerate(xs)]
        callback = ParseTreeBuilder(rules, ST).create_callback()
        lexer_conf = LexerConf(terminals, ['WS', 'COMMENT'])

        parser_conf = ParserConf(rules, callback, ['start'])
        self.parser = LALR_TraditionalLexer(lexer_conf, parser_conf)

        self.canonize_tree = CanonizeTree()

# rules_list unpacking
        # a : b (c|d) e
        #  -->
        # a : b c e | b d e
        #
        # In AST terms:
        # expansion(b, expansions(c, d), e)
        #   -->
        # expansions( expansion(b, c, e), expansion(b, d, e) )

        self._flatten(tree)

        for i, child in enumerate(tree.children):
            if isinstance(child, Tree) and child.data == 'expansions':
                tree.data = 'expansions'
                tree.children = [self.visit(ST('expansion', [option if i==j else other
                                                            for j, other in enumerate(tree.children)]))
                                    for option in dedup_list(child.children)]
                self._flatten(tree)
                break

def alias(self, tree):
        rule, alias_name = tree.children
        if rule.data == 'expansions':
            aliases = []
            for child in tree.children[0].children:
                aliases.append(ST('alias', [child, alias_name]))
            tree.data = 'expansions'
            tree.children = aliases

def _add_recurse_rule(self, type_, expr):
        if expr in self.rules_by_expr:
            return self.rules_by_expr[expr]

        new_name = '__%s_%s_%d' % (self.prefix, type_, self.i)
        self.i += 1
        t = NonTerminal(new_name)
        tree = ST('expansions', [ST('expansion', [expr]), ST('expansion', [t, expr])])
        self.new_rules.append((new_name, tree, self.rule_options))
        self.rules_by_expr[expr] = t
        return t

def literal(self, literal):
        return ST('pattern', [_literal_to_pattern(literal)])

def expr(self, rule, op, *args):
        if op.value == '?':
            empty = ST('expansion', [])
            return ST('expansions', [rule, empty])
        elif op.value == '+':
            # a : b c+ d
            #   -->
            # a : b _c d
            # _c : _c c | c;
            return self._add_recurse_rule('plus', rule)
        elif op.value == '*':
            # a : b c* d
            #   -->
            # a : b _c? d
            # _c : _c c | c;
            new_name = self._add_recurse_rule('star', rule)
            return ST('expansions', [new_name, ST('expansion', [])])
        elif op.value == '~':
            if len(args) == 1:
                mn = mx = int(args[0])

def _choice_of_rules(rules):
    return ST('expansions', [ST('expansion', [Token('RULE', name)]) for name in rules])

def maybe(self, rule):
        keep_all_tokens = self.rule_options and self.rule_options.keep_all_tokens

        def will_not_get_removed(sym):
            if isinstance(sym, NonTerminal):
                return not sym.name.startswith('_')
            if isinstance(sym, Terminal):
                return keep_all_tokens or not sym.filter_out
            assert False

        if any(rule.scan_values(will_not_get_removed)):
            empty = _EMPTY
        else:
            empty = ST('expansion', [])

        return ST('expansions', [rule, empty])

def range(self, start, end):
        assert start.type == end.type == 'STRING'
        start = start.value[1:-1]
        end = end.value[1:-1]
        assert len(_fix_escaping(start)) == len(_fix_escaping(end)) == 1, (start, end, len(_fix_escaping(start)), len(_fix_escaping(end)))
        regexp = '[%s-%s]' % (start, end)
        return ST('pattern', [PatternRE(regexp)])