Как создать и заполнить List>? - C#

    class Matrix
    {
        protected List<List<int>> matrix;
        protected readonly int ROWS, COLS;
 
        public Matrix(int rows = 3, int cols = 3)
        {
            ROWS = rows;
            COLS = cols;
            matrix = new List<List<int>>(ROWS);
            for(int i = 0; i < rows; ++i)
            {
                List<int> tmp = new List<int>(COLS);
                matrix.Add(tmp);
            }
            ;
        }
}

std::vector< std::vector<int> > matrix(3, std::vector<int>(5));