private void btnGenerateForest_Click(object sender, EventArgs e)
        {
            var fs = GetForestSpecification();

            if (fs == null)
            {
                return;
            }

            forest = ForestGenerator.Generate(fs, "^");

            var sfd = new SaveFileDialog
            {
                Filter   = "txt files (*.txt)|*.txt",
                FileName = "forest.txt"
            };

            if (sfd.ShowDialog() != DialogResult.OK)
            {
                return;
            }

            if (string.IsNullOrEmpty(sfd.FileName))
            {
                return;
            }

            ForestGenerator.SaveForestToFile(forest, sfd.FileName, false);
        }