class_docstr: An AST (a tree) for a simple arithmetic expression.
docstr: Like __str__, but always with parenthesis around each operation.
docstr_tok: ["Like","__str__",",","but","always","with","parenthesis","around","each","operation","."]
code: def tree(self):
      """
      Like __str__, but always with parenthesis around each operation.
      """
      op = self.op
      if op == "minus":
          return f"(-{self.args[0].tree()})"
      return f"({self.args[0].tree()} {op} {self.args[1].tree()})"
  
imports: import random
label_desc: Use image node_id 7 for calling the Expression obj's underlying member method code with example usage: obj.tree() and returns: str, self, str, op, str, self, str, str, self, str