美式有没有一种可能，折现到0时刻，直接应该行权？

问题如下：

What is the difference between using a binomial tree to value an American option and using it to value the corresponding European option?

解释：

In the case of an American option, we have to check at each node whether the option should be exercised. The value at a node is the greater of the intrinsic value of the option and the result of rolling back from the subsequent nodes.