Array in Array example

.sol

pragma solidity >=0.8.9;

contract Test {
 
 uint256[][20] public array;

 mapping(uint256 => bool) private _exists;

  function push(uint256 index, uint256 indexChildren, uint256 value) external {
    bool exists = _exists[index];



    if (!exists) {
      uint256[] memory newArray = new uint256[](20);
      array[index] = newArray;
      _exists[index] = true;
    }

    uint256[] memory storedArray = array[index];

    storedArray[indexChildren] = value;

    array[index] = storedArray;
  }
}