diff --git a/trees/BIT.cc b/trees/BIT.cc
new file mode 100644
index 0000000..4773048
--- /dev/null
+++ b/trees/BIT.cc
@@ -0,0 +1,22 @@
+#include "../include.hh"
+
+template<typename T>
+struct BIT {
+    int n;
+    vector<T> c;
+    BIT(size_t n) : n(n), c(n + 1) {}
+    void add(size_t i, const T& k) {
+        while (i <= n) {
+            c[i] += k;
+            i += lowbit(i);
+        }
+    }
+    T getsum(size_t i) {
+        T res = {};
+        while (i) {
+            res += c[i];
+            i -= lowbit(i);
+        }
+        return res;
+    }
+};