如何通过解析字符串生成树形结构？

class Node:
    def __init__(self, value):
        self.value = value
        self.children = []

def generate_tree(string):
    stack = []
    root = None

    for char in string:
        if char == '(':
            if stack:
                node = Node('')
                stack[-1].children.append(node)
                stack.append(node)
            else:
                root = Node('')
                stack.append(root)
        elif char == ')':
            stack.pop()
        else:
            stack[-1].value += char

    return root

string = "(A(B(C))(D))"
tree = generate_tree(string)

     A
    / \
   B   D
  /
 C