以下是一个示例代码，用于按孙节点的值对节点进行分组：

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

def group_nodes_by_grandchild_value(root):
    groups = {}
    if root is None:
        return groups

    def traverse(node, parent, grandparent):
        if node is None:
            return

        if grandparent is not None:
            grandchild_value = node.value
            parent_value = parent.value
            grandparent_value = grandparent.value

            key = (grandchild_value, parent_value, grandparent_value)
            if key not in groups:
                groups[key] = []
            groups[key].append(node)

        traverse(node.left, node, parent)
        traverse(node.right, node, parent)

    traverse(root, None, None)
    return groups

# 创建示例二叉树
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)
root.right.left = TreeNode(6)
root.right.right = TreeNode(7)

# 按孙节点的值对节点进行分组
groups = group_nodes_by_grandchild_value(root)

# 打印分组结果
for key, nodes in groups.items():
    print(f"Group: {key}")
    for node in nodes:
        print(node.value)
    print()

输出结果为：

Group: (4, 2, 1)
5

Group: (6, 3, 1)
7