diff --git a/cs/kth-largest-sum-in-a-binary-tree.cs b/cs/kth-largest-sum-in-a-binary-tree.cs
new file mode 100644
index 0000000..c0a11cd
--- /dev/null
+++ b/cs/kth-largest-sum-in-a-binary-tree.cs
@@ -0,0 +1,27 @@
+public class Solution {
+    private void Sum(List<long> levels, TreeNode node, int level) {
+        if (node == null) {
+            return;
+        }
+
+        while (level >= levels.Count) {
+            levels.Add(0);
+        }
+
+        levels[level] += node.val;
+        Sum(levels, node.left, level + 1);
+        Sum(levels, node.right, level + 1);
+    }
+
+    public long KthLargestLevelSum(TreeNode root, int k) {
+        var levels = new List<long>();
+
+        Sum(levels, root, 0);
+        if (k > levels.Count) {
+            return -1;
+        }
+
+        levels.Sort();
+        return levels[levels.Count - k];
+    }
+}