diff --git a/homework4/BiTree.cpp b/homework4/BiTree.cpp
index 11f1f34..d99090d 100644
--- a/homework4/BiTree.cpp
+++ b/homework4/BiTree.cpp
@@ -1 +1,26 @@
 #include "BiTree.h"
+
+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) {
+        return true;
+    }
+    return false;
+}
+
+int BiTree::sum_leaf(BiTree *bt) {
+    if(is_empty(bt)) {
+        return 0;
+    }
+    if(is_leaf(bt)) {
+        return bt->data;
+    }
+    return sum_leaf(bt->left)+sum_leaf(bt->right);
+}
+
diff --git a/homework4/BiTree.h b/homework4/BiTree.h
index b63eb58..eb7c2b7 100644
--- a/homework4/BiTree.h
+++ b/homework4/BiTree.h
@@ -4,7 +4,14 @@
 
 
 class BiTree {
+public:
+    int data;
+    BiTree *left;
+    BiTree *right;
 
+    static bool is_empty(BiTree *bt);
+    static bool is_leaf(BiTree *bt);
+    static int sum_leaf(BiTree *bt);
 };
 
 
diff --git a/homework4/test1.cpp b/homework4/test1.cpp
index e69de29..9b4b27e 100644
--- a/homework4/test1.cpp
+++ b/homework4/test1.cpp
@@ -0,0 +1,32 @@
+#include<iostream>
+#include"BiTree.h"
+using namespace std;
+
+BiTree* createNode(int data) {
+    BiTree* newNode = new BiTree();
+    newNode->data = data;
+    newNode->left = nullptr;
+    newNode->right = nullptr;
+    return newNode;
+}
+
+void createTree(BiTree*& bt, int value) {
+    if (bt == nullptr) {
+        bt = createNode(value);
+    } else {
+        if (value < bt->data) {
+            createTree(bt->left, value);
+        } else if (value > bt->data) {
+            createTree(bt->right, value);
+        }
+    }
+}
+
+int main() {
+    BiTree* root = nullptr;
+    for (int i = 0; i < 10; i++) {
+        createTree(root, i);
+    }
+    cout << BiTree::sum_leaf(root) << endl;
+    return 0;
+}
\ No newline at end of file