diff --git a/README.md b/README.md
index 32803eb..0ea4c3b 100644
--- a/README.md
+++ b/README.md
@@ -440,7 +440,7 @@ Then test it out on a computer to make sure it's not buggy from syntax.
         - [x] heap_sort() - take an unsorted array and turn it into a sorted array in-place using a max heap
             - note: using a min heap instead would save operations, but double the space needed (cannot do in-place).
 
-- [ ] **Balanced search trees**
+- [x] **Balanced search trees**
     - Know least one type of balanced binary tree (and know how it's implemented):
     - "Among balanced search trees, AVL and 2/3 trees are now passé, and red-black trees seem to be more popular.
         A particularly interesting self-organizing data structure is the splay tree, which uses rotations