diff --git a/src/main/java/com/github/hcsp/functional/Order.java b/src/main/java/com/github/hcsp/functional/Order.java
index 6df18c4..657d241 100644
--- a/src/main/java/com/github/hcsp/functional/Order.java
+++ b/src/main/java/com/github/hcsp/functional/Order.java
@@ -3,6 +3,7 @@
 import java.math.BigDecimal;
 import java.time.Instant;
 import java.util.Arrays;
+import java.util.Comparator;
 import java.util.List;
 import java.util.TreeSet;
 
@@ -58,7 +59,13 @@ public String toString() {
     // 2.然后按照订单金额排序，订单金额大的靠前；
     // 3.然后按照下单时间排序，下单时间早的靠前
     public static TreeSet<Order> toTreeSet(List<Order> orders) {
-        return null;
+        Comparator<Order> compareOrders = Comparator.comparing(Order::isOpen,Boolean::compareTo).reversed().
+                thenComparing(Order::getOrderTime,Instant::compareTo).
+                thenComparing(Order::getId,Integer::compareTo);
+        TreeSet<Order> result = new TreeSet<>(compareOrders);
+        result.addAll(orders);
+        return result;
+
     }
 
     public static void main(String[] args) {