diff --git a/bintree.c b/bintree.c
index 5cf82a9..1686c2b 100644
--- a/bintree.c
+++ b/bintree.c
@@ -1,36 +1,117 @@
 #include <string.h>
+#include <stdlib.h>
 #include "stack.h"
 #include "bintree.h"
 
-//TODO: binären Suchbaum implementieren
-/*  * `addToTree`: fügt ein neues Element in den Baum ein (rekursiv),
-    * `clearTree`: gibt den gesamten Baum frei (rekursiv),
-    * `treeSize`: zählt die Knoten im Baum (rekursiv),
-    * `nextTreeData`: Traversierung mit Hilfe des zuvor implementierten Stacks. */
+static StackNode *iterStack = NULL;
+static void pushLeftBranch(StackNode **stack, TreeNode *node);
 
-// Adds a copy of data's pointer destination to the tree using compareFct for ordering. Accepts duplicates
-// if isDuplicate is NULL, otherwise ignores duplicates and sets isDuplicate to 1 (or to 0 if a new entry is added).
-TreeNode *addToTree(TreeNode *root, const void *data, size_t dataSize, CompareFctType compareFct, int *isDuplicate)
+// Inserts a new node into the BST.
+// If isDuplicate == NULL → duplicates are allowed
+// If isDuplicate != NULL → duplicates are ignored and *isDuplicate = 1
+TreeNode *addToTree(TreeNode *root, const void *data, size_t dataSize,
+                    CompareFctType compareFct, int *isDuplicate)
 {
+    if (root == NULL)
+    {
+        TreeNode *newNode = calloc(1, sizeof(TreeNode));
+        if (!newNode)
+            return NULL;
 
+        newNode->data = malloc(dataSize);
+        if (!newNode->data)
+        {
+            free(newNode);
+            return NULL;
+        }
+
+        memcpy(newNode->data, data, dataSize);
+
+        if (isDuplicate)
+            *isDuplicate = 0;
+
+        return newNode;
+    }
+
+    int cmp = compareFct(data, root->data);
+
+    if (cmp < 0 || (cmp == 0 && isDuplicate == NULL))
+    {
+        root->left = addToTree(root->left, data, dataSize, compareFct, isDuplicate);
+    }
+    else if (cmp > 0)
+    {
+        root->right = addToTree(root->right, data, dataSize, compareFct, isDuplicate);
+    }
+    else
+    {
+        if (isDuplicate)
+            *isDuplicate = 1;
+    }
+
+    return root;
 }
 
-// Iterates over the tree given by root. Follows the usage of strtok. If tree is NULL, the next entry of the last tree given is returned in ordering direction.
-// Use your implementation of a stack to organize the iterator. Push the root node and all left nodes first. On returning the next element,
-// push the top node and push all its left nodes.
+static void pushLeftBranch(StackNode **stack, TreeNode *node)
+{
+    while (node)
+    {
+        *stack = push(*stack, node);
+        node = node->left;
+    }
+}
+
+// If root != NULL → reset iterator and start from new tree.
+// If root == NULL → continue iterating.
 void *nextTreeData(TreeNode *root)
 {
+    // Start new iteration
+    if (root != NULL)
+    {
+        // reset old iterator state
+        clearStack(iterStack);
+        iterStack = NULL;
 
+        // push root and all left children
+        pushLeftBranch(&iterStack, root);
+    }
+
+    // No active iterator
+    if (iterStack == NULL)
+        return NULL;
+
+    // Get next node
+    TreeNode *node = (TreeNode *)top(iterStack);
+    iterStack = pop(iterStack);
+
+    // push right subtree and its left descendants
+    if (node->right)
+        pushLeftBranch(&iterStack, node->right);
+
+    return node->data;
 }
 
-// Releases all memory resources (including data copies).
+// Frees all nodes and also resets iterator.
 void clearTree(TreeNode *root)
 {
+    if (!root)
+        return;
 
+    clearTree(root->left);
+    clearTree(root->right);
+
+    free(root->data);
+    free(root);
+
+    // If we clear the tree, iterator must not point into freed memory.
+    clearStack(iterStack);
+    iterStack = NULL;
 }
 
-// Returns the number of entries in the tree given by root.
 unsigned int treeSize(const TreeNode *root)
 {
+    if (!root)
+        return 0;
 
-}
\ No newline at end of file
+    return 1 + treeSize(root->left) + treeSize(root->right);
+}
diff --git a/test_bintree.c b/test_bintree.c
index 3ca280d..2f2ba5e 100644
--- a/test_bintree.c
+++ b/test_bintree.c
@@ -1,39 +1,145 @@
 #include "unity.h"
 #include "bintree.h"
-#include "string.h"
+#include <string.h>
+#include <stdio.h>
+
+static int compareInt(const void *a, const void *b)
+{
+    int x = *(const int *)a;
+    int y = *(const int *)b;
+    return (x > y) - (x < y);
+}
 
 void setUp(void)
 {
-    // set stuff up here
 }
 
 void tearDown(void)
 {
-    // set stuff up here
 }
 
-// this adds some strings and checks if they are returned in the right order
-void test_insert_and_retrieve(void)
+/* ============================================================
+   TEST 1 — Strings einfügen + korrekte Reihenfolge prüfen
+   ============================================================ */
+
+void test_insert_and_retrieve_strings(void)
 {
     char *data1 = "a_this";
     char *data2 = "b_is";
     char *data3 = "c_testdata";
 
-    TreeNode *root = addToTree(NULL, data1, strlen(data1) + 1, (CompareFctType)&strcmp, NULL);
-    addToTree(root, data2, strlen(data2) + 1, (CompareFctType)&strcmp, NULL);
-    addToTree(root, data3, strlen(data3) + 1, (CompareFctType)&strcmp, NULL);
+    TreeNode *root = addToTree(NULL, data1, strlen(data1) + 1, (CompareFctType)strcmp, NULL);
+    addToTree(root, data2, strlen(data2) + 1, (CompareFctType)strcmp, NULL);
+    addToTree(root, data3, strlen(data3) + 1, (CompareFctType)strcmp, NULL);
 
-    TEST_ASSERT_EQUAL_STRING(data1, (char *)nextTreeData(root));
-    TEST_ASSERT_EQUAL_STRING(data2, (char *)nextTreeData(NULL));
-    TEST_ASSERT_EQUAL_STRING(data3, (char *)nextTreeData(NULL));
+    TEST_ASSERT_EQUAL_STRING(data1, nextTreeData(root));
+    TEST_ASSERT_EQUAL_STRING(data2, nextTreeData(NULL));
+    TEST_ASSERT_EQUAL_STRING(data3, nextTreeData(NULL));
+    TEST_ASSERT_EQUAL_PTR(NULL, nextTreeData(NULL)); // Ende
 
     clearTree(root);
 }
 
+/* ============================================================
+   TEST 2 — Integer einfügen + Traversierung
+   ============================================================ */
+
+void test_insert_and_retrieve_ints(void)
+{
+    int a = 2, b = 1, c = 3;
+
+    TreeNode *root = NULL;
+    root = addToTree(root, &a, sizeof(int), compareInt, NULL);
+    addToTree(root, &b, sizeof(int), compareInt, NULL);
+    addToTree(root, &c, sizeof(int), compareInt, NULL);
+
+    int *v1 = nextTreeData(root);
+    int *v2 = nextTreeData(NULL);
+    int *v3 = nextTreeData(NULL);
+    int *v4 = nextTreeData(NULL);
+
+    TEST_ASSERT_EQUAL_INT(1, *v1);
+    TEST_ASSERT_EQUAL_INT(2, *v2);
+    TEST_ASSERT_EQUAL_INT(3, *v3);
+    TEST_ASSERT_NULL(v4);
+
+    clearTree(root);
+}
+
+/* ============================================================
+   TEST 3 — treeSize korrekt?
+   ============================================================ */
+
+void test_tree_size(void)
+{
+    TreeNode *root = NULL;
+
+    TEST_ASSERT_EQUAL_UINT(0, treeSize(root));
+
+    int x1 = 10, x2 = 5, x3 = 15;
+    root = addToTree(root, &x1, sizeof(int), compareInt, NULL);
+    addToTree(root, &x2, sizeof(int), compareInt, NULL);
+    addToTree(root, &x3, sizeof(int), compareInt, NULL);
+
+    TEST_ASSERT_EQUAL_UINT(3, treeSize(root));
+
+    clearTree(root);
+}
+
+/* ============================================================
+   TEST 4 — Duplikaterkennung
+   ============================================================ */
+
+void test_duplicate_detection(void)
+{
+    int x = 42;
+    int dupFlag = -1;
+
+    TreeNode *root = addToTree(NULL, &x, sizeof(int), compareInt, &dupFlag);
+    TEST_ASSERT_EQUAL_INT(0, dupFlag);
+
+    addToTree(root, &x, sizeof(int), compareInt, &dupFlag);
+    TEST_ASSERT_EQUAL_INT(1, dupFlag);
+
+    TEST_ASSERT_EQUAL_UINT(1, treeSize(root));
+
+    clearTree(root);
+}
+
+/* ============================================================
+   TEST 5 — Iterator nach clearTree → sollte NULL liefern
+   ============================================================ */
+
+void test_iterator_after_cleartree(void)
+{
+    int a = 5, b = 1, c = 9;
+
+    TreeNode *root = NULL;
+    root = addToTree(root, &a, sizeof(int), compareInt, NULL);
+    addToTree(root, &b, sizeof(int), compareInt, NULL);
+    addToTree(root, &c, sizeof(int), compareInt, NULL);
+
+    nextTreeData(root);
+
+    clearTree(root);
+
+    TEST_ASSERT_NULL(nextTreeData(NULL));
+    TEST_ASSERT_NULL(nextTreeData(NULL));
+}
+
 int main(void)
 {
-    printf("============================\nBintree tests\n============================\n");
+    printf("============================\n");
+    printf("Bintree tests\n");
+    printf("============================\n");
+
     UNITY_BEGIN();
-    RUN_TEST(test_insert_and_retrieve);
+
+    RUN_TEST(test_insert_and_retrieve_strings);
+    RUN_TEST(test_insert_and_retrieve_ints);
+    RUN_TEST(test_tree_size);
+    RUN_TEST(test_duplicate_detection);
+    RUN_TEST(test_iterator_after_cleartree);
+
     return UNITY_END();
-}
\ No newline at end of file
+}