Add test script for nested BehaviorTree field.

Author: bianjingshiyi

Assets/Samples/BehaviorTreeList.cs

@@ -1,4 +1,5 @@
 using CleverCrow.Fluid.BTs.Trees;
+using System;
 using System.Collections.Generic;
 using UnityEngine;
 
@@ -10,12 +11,20 @@ protected void Awake()
         {
             for (int i = 0; i < 3; i++)
             {
-                trees.Add(new BehaviorTreeBuilder(gameObject).Name($"Tree{i}").Sequence()
-                    .WaitTime(1)
-                    .ReturnSuccess()
-                .End().Build());
+                trees.Add(new NestedTree()
+                {
+                    tree = new BehaviorTreeBuilder(gameObject).Name($"Tree{i}").Sequence()
+                        .WaitTime(1)
+                        .ReturnSuccess()
+                    .End().Build()
+                });
             }
         }
-        public List<BehaviorTree> trees = new List<BehaviorTree>();
+        public List<NestedTree> trees = new List<NestedTree>();
+    }
+    [Serializable]
+    public class NestedTree
+    {
+        public BehaviorTree tree;
     }
 }