avl_tree: memory released, valgrind says “no leaks are possible”

src/lol/algorithm/avl_tree.h

@@ -52,6 +52,15 @@ public:
         return this->m_root->exists(key);
     }
 
+    virtual ~avl_tree()
+    {
+        if (this->m_root)
+        {
+            this->m_root->cascade_delete();
+            delete this->m_root;
+        }
+    }
+
 protected:
 
     class tree_node
@@ -169,6 +178,21 @@ protected:
             return false;
         }
 
+        void cascade_delete()
+        {
+            if (this->m_child[0])
+            {
+                this->m_child[0]->cascade_delete();
+                delete this->m_child[0];
+            }
+
+            if (this->m_child[1])
+            {
+                this->m_child[1]->cascade_delete();
+                delete this->m_child[1];
+            }
+        }
+
         int get_balance()
         {
             return this->m_stairs[1] - this->m_stairs[0];

src/t/algorithm/avl_tree.cpp

@@ -20,6 +20,7 @@ namespace lol
 class test_tree : public avl_tree<int, int>
 {
 public:
+    virtual ~test_tree() {}
 
 	int get_root_balance()
 	{