56544301.cs

var name = "directory name";
var path = @"c:\temp\dirtest";

for (int i = 0; i < 12; i++)
{
	CreateDirectory(name, path);
}

void CreateDirectory(string directoryName, string filePath)
{
	var basePath = Path.Combine(filePath, directoryName);
	if (!Directory.Exists(basePath))
	{
		Directory.CreateDirectory(basePath);
		return;
	}

	/*
	"directory name"
	"directory name (1)"
	"directory name (2)"
	etc
	*/
	var matches = Directory.GetDirectories(path, $"{directoryName} (*)");
	Directory.CreateDirectory(Path.Combine(filePath, directoryName + $" ({matches.Length + 1})"));
}