MerkleTree.sol

...
import "@openzeppelin/contracts/utils/cryptography/MerkleProof.sol";

contract MyToken is ERC721, Ownable {
    
    bytes32 rootHash = '0x...'
    mapping(address => uint256) tokenCount;
    
    ... 

    function whitelistMint(address to, bytes32[] proof) public onlyOwner {
        require(MerkleProof.verify(proof, rootHash, keccak256(msg.sender), "ADDRESS NOT IN WHITELIST");
        ... // implementation
        _safeMint(to, tokenId);
    }
    
    function setHash(bytes32 _hash) { ... }
}