Initialize a Merkle tree of 8 with blank leaves in solidity

Question

I am trying to initialise an empty merkle tree in the constructor my solidity contract I have a merkle tree of 8 leaves, so that means that the flattened out form of the merkle tree would be something like uint256 [15] hashes. But i want to initalize it in the constructor. The first 8 leaves will be 0 and we can assume they're already hashed. after that there will be 4 nodes which would be hashes of the leaves and then 2 and then the root. How can I implement this using poseidon hash? Thanks.