diff --git a/code/decision_tree.py b/code/decision_tree.py
index 8ad3337..406b2fb 100644
--- a/code/decision_tree.py
+++ b/code/decision_tree.py
@@ -5,22 +5,44 @@
 
 
 class TreeNode:
-    def __init__(self, data_idx, depth, child_lst=[]):
+    def __init__(self, data_idx, depth, child_lst=None):
+        """
+        Initialize a TreeNode object.
+
+        Parameters:
+        - data_idx (int): Index of the data associated with the node.
+        - depth (int): Depth of the node in the tree.
+        - child_lst (list, optional): List of child nodes. Defaults to an empty list.
+        """
         self.data_idx = data_idx
         self.depth = depth
-        self.child = child_lst
+        self.child = child_lst if child_lst is not None else []
         self.label = None
         self.split_col = None
         self.child_cate_order = None
 
     def set_attribute(self, split_col, child_cate_order=None):
+        """
+        Set the attributes of the node.
+
+        Parameters:
+        - split_col: Column used for splitting the data.
+        - child_cate_order (list, optional): Order of child categories. Defaults to None.
+        """
         self.split_col = split_col
         self.child_cate_order = child_cate_order
 
     def set_label(self, label):
+        """
+        Set the label for the node.
+
+        Parameters:
+        - label: The label to be assigned to the node.
+        """
         self.label = label
 
 
+
 class DecisionTree(metaclass=ABCMeta):
     def __init__(self, max_depth, min_sample_leaf, min_split_criterion=1e-4, verbose=False):
         self.max_depth = max_depth
@@ -296,4 +318,4 @@ def get_nex_node(self, node: TreeNode, x: np.array):
     if tree_type == "classification":
         print(classification_report(y_true=y_test, y_pred=y_pred))
     else:
-        print(mean_squared_error(y_test, y_pred))
\ No newline at end of file
+        print(mean_squared_error(y_test, y_pred))