diff --git a/src/tree.py b/src/tree.py
index 834db61992782bd64f77d5b873b593e637e9a7a3..25593b310bf2d8388fd6b05937f3ecfa09d4df75 100644
--- a/src/tree.py
+++ b/src/tree.py
@@ -1,4 +1,3 @@
-# -*- coding: utf-8 -*-
 import logging
 from genericpath import exists
 import json
@@ -17,7 +16,7 @@ logger.addHandler(handler)
 
 
 def load_json(p):
-    with open(p, 'r', encoding='utf-8') as f:
+    with open(p, 'r') as f:
         return json.loads(f.read())
 
 
@@ -30,7 +29,7 @@ def dump_json(p, j, exist_ok=False, override=False):
             logger.error(f"{p} already exist")
             sys.exit(0)
 
-    with open(p, 'w+', encoding='utf-8') as f:
+    with open(p, 'w+', encoding="utf8") as f:
         f.write(json.dumps(j, indent=2, ensure_ascii=False))
 
 
@@ -92,18 +91,16 @@ class TreeWalker:
         for index, level in enumerate(root_node["children"]):
             level_title = list(level.keys())[0]
             level_node = list(level.values())[0]
-            level_path = os.path.join(self.root, f"{index+1}.{level_title}")
+            level_path = os.path.join(self.root, f"{index + 1}.{level_title}")
             self.load_chapters(level_path, level_node)
             for index, chapter in enumerate(level_node["children"]):
                 chapter_title = list(chapter.keys())[0]
                 chapter_node = list(chapter.values())[0]
-                chapter_path = os.path.join(
-                    level_path, f"{index+1}.{chapter_title}")
+                chapter_path = os.path.join(level_path, f"{index + 1}.{chapter_title}")
                 self.load_sections(chapter_path, chapter_node)
                 for index, section_node in enumerate(chapter_node["children"]):
                     section_title = list(section_node.keys())[0]
-                    full_path = os.path.join(
-                        chapter_path, f"{index+1}.{section_title}")
+                    full_path = os.path.join(chapter_path, f"{index + 1}.{section_title}")
                     if os.path.isdir(full_path):
                         self.ensure_exercises(full_path)
 
@@ -111,6 +108,11 @@ class TreeWalker:
         dump_json(tree_path, self.tree, exist_ok=True, override=True)
         return self.tree
 
+    def sort_dir_list(self, dirs):
+        result = [self.extract_node_env(dir) for dir in dirs]
+        result.sort(key=lambda item: item[0])
+        return result
+
     def load_levels(self, root_node):
         levels = []
         for level in os.listdir(self.root):
@@ -167,7 +169,7 @@ class TreeWalker:
         for index, [number, element] in enumerate(children):
             title = list(element.keys())[0]
             origin = os.path.join(base, f"{number}.{title}")
-            posted = os.path.join(base, f"{index+1}.{title}")
+            posted = os.path.join(base, f"{index + 1}.{title}")
             if origin != posted:
                 self.logger.info(f"rename [{origin}] to [{posted}]")
             os.rename(origin, posted)
@@ -241,8 +243,12 @@ class TreeWalker:
         return config
 
     def ensure_node_id(self, config):
-        if "node_id" not in config:
-            config["node_id"] = self.gen_node_id()
+        if "node_id" not in config or \
+                not config["node_id"].startswith(f"{self.tree}-") or \
+                config["node_id"] in id_set:
+            new_id = self.gen_node_id()
+            id_set.add(new_id)
+            config["node_id"] = new_id
             return True, config
         else:
             return False, config
@@ -258,7 +264,8 @@ class TreeWalker:
             return int(number), title
         except Exception as error:
             self.logger.error(f"目录 [{path}] 解析失败，结构不合法，可能是缺少序号")
-            sys.exit(1)
+            # sys.exit(1)
+            raise error
 
     def load_chapter_node(self, full_name):
         config = self.ensure_chapter_config(full_name)