diff --git a/01-tree_successor/task.md b/01-tree_successor/task.md
index 61a60b1b4e9804e9020af9c0ad02d3e776a6b3ba..4b11338d520a6a5f55552111340e39c7f8ec9890 100644
--- a/01-tree_successor/task.md
+++ b/01-tree_successor/task.md
@@ -6,3 +6,5 @@ and it should return another node of the tree with the next higher key
 - If there is no such node, it should return a null pointer.
 - The given node can also be a null pointer, in which case the method should
   return the smallest node in the tree.
+
+You should submit the file `tree_successor.h`.