MerkleTreeAllowlist.sol

contract YourNFTContract is ERC721 {
  bytes32 private _allowlistMerkleRoot;

  function setMerkleRoot(bytes32 newRoot) external onlyOwner {
    _allowlistMerkleRoot = newRoot;
  }

  modifier onlyIfValidMerkleProof(bytes32[] calldata proof) {
    // leaf is just the address of the sender
    bytes32 leaf = keccak256(abi.encodePacked(msg.sender));

    // compute hash
    bytes32 computedHash = leaf;
    for (uint256 i = 0; i < proof.length; i++) {
        bytes32 proofElement = proof[i];
        if (computedHash <= proofElement) {
            // Hash(current computed hash + current element of the proof)
            computedHash = _efficientHash(computedHash, proofElement);
        } else {
            // Hash(current element of the proof + current computed hash)
            computedHash = _efficientHash(proofElement, computedHash);
        }
    }

    // compare the resulting hash to root
    if (computedHash != _allowlistMerkleRoot) revert MerkleProofInvalid();
    _;
  }

  function allowlistedMint(bytes32[] calldata merkleProof)
    external
    payable
    onlyIfValidMerkleProof(merkleProof)
  {
    // your mint logic
  }
}