Destructor not working

[Ey80oG1T]

So I'm making a SLL class, however, it appears that I have some memory leaks. Here's the code that's causing problems:

// used to detect memory leaks in Visual Studio
#ifdef _DEBUG
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
#define DEBUG_NEW new(_NORMAL_BLOCK, __FILE__, __LINE__)
#define new DEBUG_NEW
#endif

class sll
{
private:
	struct Node
	{
		int val;
		Node* next;
	};

private:
	Node* head;

public:
	sll()
		: head(nullptr) {}

	~sll()
	{
		Node* node_ptr = head;
		while (head != nullptr)
		{
			node_ptr = node_ptr->next;
			delete head;
			head = node_ptr;
		}
	}

public:
	void insert_back(int val)
	{
		if (head == nullptr)
		{
			head = new Node{ val, nullptr };
			return;
		}

		Node* node_ptr = head;
		while (node_ptr->next != nullptr)
			node_ptr = node_ptr->next;

		node_ptr->next = new Node{ val, node_ptr->next };
	}
};

int main()
{
	sll list;
	list.insert_back(1);
	list.insert_back(2);
	list.insert_back(3);

        // logs memory leaks for Visual Studio
	_CrtDumpMemoryLeaks();
}

When I run the code, it tells me I have three leaks, one for each insert. But why is this? How did I mess up on my destructor?

Also, yes, it's better to use smart pointers, but I'm using raw pointers for now.

[helios]

The destructor has yet to run at line 62. list is still in scope.

[dutch]

Yeah, just put braces around lines 56 to 59.

And if you want to be able to append to the back of the list you should maintain a tail pointer.