diff --git a/bintree.c b/bintree.c
index ece271f..82791ee 100644
--- a/bintree.c
+++ b/bintree.c
@@ -68,8 +68,29 @@ TreeNode *addToTree(TreeNode *root, const void *data, size_t dataSize, CompareFc
 // push the top node and push all its left nodes.
 void *nextTreeData(TreeNode *root)
 {
+    static StackNode *stack = NULL;
+    static TreeNode *current = NULL;
 
-}
+    if(root != NULL){
+        clearStack(stack);
+        stack = NULL;
+        current = root;
+    }
+
+    while (current != NULL)
+    {
+        stack = push(stack, current);
+        current = current->left;
+    }
+
+    TreeNode *node = (TreeNode *)top(stack);
+    stack = pop(stack);
+
+    current = node->right;
+
+    return node->data;
+    
+} 
 
 // Releases all memory resources (including data copies).
 void clearTree(TreeNode *root)