diff --git a/homework4/BiTree.cpp b/homework4/BiTree.cpp
index 6faab55..52d48ca 100644
--- a/homework4/BiTree.cpp
+++ b/homework4/BiTree.cpp
@@ -1,65 +1,87 @@
 #include "BiTree.h"
 #include <sstream>
 
-bool BiTree::is_empty(BiTree *bt) {
-    if (bt == nullptr) {
+bool BiTree::is_empty(BiTree* bt)
+{
+    if (bt == nullptr)
+    {
         return true;
     }
     return false;
 }
 
-bool BiTree::is_leaf(BiTree *bt) {
-    if (bt->left == nullptr && bt->right == nullptr) {
+bool BiTree::is_leaf(BiTree* bt)
+{
+    if (bt->left == nullptr && bt->right == nullptr)
+    {
         return true;
     }
     return false;
 }
 
-int BiTree::sum_leaf(BiTree *bt) {
-    if (is_empty(bt)) {
+int BiTree::sum_leaf(BiTree* bt)
+{
+    if (is_empty(bt))
+    {
         return 0;
     }
-    if (is_leaf(bt)) {
+    if (is_leaf(bt))
+    {
         return bt->data;
     }
     return sum_leaf(bt->left) + sum_leaf(bt->right);
 }
 
-BiTree *BiTree::createNode(int data) {
-    BiTree *newNode = new BiTree();
+BiTree* BiTree::createNode(int data)
+{
+    BiTree* newNode = new BiTree();
     newNode->data = data;
     newNode->left = nullptr;
     newNode->right = nullptr;
     return newNode;
 }
 
-void BiTree::insertNode(BiTree *&bt, int value) {
-    if (bt == nullptr) {
+void BiTree::insertNode(BiTree*& bt, int value)
+{
+    if (bt == nullptr)
+    {
         bt = createNode(value);
-    } else {
-        if (value < bt->data) {
+    }
+    else
+    {
+        if (value < bt->data)
+        {
             insertNode(bt->left, value);
-        } else if (value > bt->data) {
+        }
+        else if (value > bt->data)
+        {
             insertNode(bt->right, value);
         }
     }
 }
 
 
-void toStringHelper(const BiTree *node, std::ostringstream &oss, const std::string &prefix, bool isLeft) {
-    if (node != nullptr) {
+void toStringHelper(const BiTree* node, std::ostringstream& oss, const std::string& prefix, bool isLeft,
+                    bool hasSibling)
+{
+    if (node != nullptr)
+    {
         oss << prefix;
 
-        oss << (isLeft ? "|--" : "|--") << node->data << "\n";
+        oss << (isLeft ? (hasSibling ? "├─" : "└─") : (hasSibling ? "├─" : "└─")) << node->data << "\n";
 
-        std::string newPrefix = prefix + (isLeft ? "|   " : "    ");
-        toStringHelper(node->left, oss, newPrefix, true);
-        toStringHelper(node->right, oss, newPrefix, false);
+        std::string newPrefix = prefix + (isLeft ? (hasSibling ? "│  " : "   ") : "   ");
+        bool hasLeftSibling = (node->left != nullptr && node->right != nullptr);
+
+        toStringHelper(node->left, oss, newPrefix, true, hasLeftSibling);
+        toStringHelper(node->right, oss, newPrefix, false, false);
     }
 }
 
-std::string BiTree::toString() {
+std::string BiTree::toString()
+{
     std::ostringstream oss;
-    toStringHelper(this, oss, "", false);
+    toStringHelper(this, oss, "", false, false);
     return oss.str();
 }
+