left->father = right->father = father;

struct cluster {
    shared_ptr<cluster> left,right;
    weak_ptr<cluster> father;
    cluster(){}
    cluster(shared_ptr<cluster>& left,shared_ptr<cluster>& right) {
        this->left = left;
        this->right = right;
    }
};
int main() {
    auto left = make_shared<cluster>();
    auto right = make_shared<cluster>();
    auto father = make_shared<cluster>(left,right);
    left->father = right->father = father;
    return 0;
}