MoreInformation.sol

... // import statements

contract MyToken is ERC721, Ownable {
    // vars
    
    function _convertLeaf(address _user, uint256 _quantity)
        internal
        pure
        returns (bytes32)
    {
        string memory quantity_string = Strings.toString(_quantity);
        string memory address_string = Strings.toHexString(
            uint256(uint160(_user)),
            20
        );
        return keccak256(abi.encodePacked(quantity_string, address_string));
    }
    
    function preSaleMint(uint256 _quantity, bytes32[] calldata _proof, uint256 _maxQuantity, bytes32 _leaf) external payable callerIsUser {
      ...

        require(
            _convertLeaf(msg.sender, _maxQuantity) == _leaf,
            "LEAF NODE AND QUANTITY DO NOT MATCH"
        );
        bool isValidProof = MerkleProof.verify(
            _proof,
            preSaleMerkleRoot,
            _leaf
        );
        require(isValidProof, "INVALID PROOF");
        
        ... // implementation here


        _safeMint(msg.sender, _quantity);
    }
}