diff --git a/book.py b/book.py
index 3493698..cb949af 100644
--- a/book.py
+++ b/book.py
@@ -144,12 +144,9 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
     state_string = state.translated('state')
 
     parent = fields.Many2One(string="Parent",
-        model_name='cashbook.book', ondelete='RESTRICT',
-        left='left', right='right')
+        model_name='cashbook.book', ondelete='RESTRICT')
     childs = fields.One2Many(string='Children', field='parent',
         model_name='cashbook.book')
-    left = fields.Integer(string='Left', required=True, select=True)
-    right = fields.Integer(string='Right', required=True, select=True)
 
     @classmethod
     def __register__(cls, module_name):
@@ -157,6 +154,8 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
 
         table = cls.__table_handler__(module_name)
         table.drop_column('start_balance')
+        table.drop_column('left')
+        table.drop_column('right')
 
     @classmethod
     def __setup__(cls):
@@ -189,14 +188,6 @@ class Book(tree(separator='/'), Workflow, ModelSQL, ModelView):
                 },
             })
 
-    @staticmethod
-    def default_left():
-        return 0
-
-    @staticmethod
-    def default_right():
-        return 0
-
     @classmethod
     def default_number_atcheck(cls):
         return True