如何在不覆盖以前输入的值的情况下使用整数列表创建树

class TreeNode:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None

def build_tree(nums, start):
    if start >= len(nums) or nums[start] is None:
        return None

    root = TreeNode(nums[start])
    root.left = build_tree(nums, 2 * start + 1)
    root.right = build_tree(nums, 2 * start + 2)

    return root

nums = [1, 2, 3, None, 4, 5]
root = build_tree(nums, 0)