//http://stackoverflow.com/questions/43449629/split-mathematical-formula-based-on-level-in-c-sharp

//https://regex101.com/r/4hf2W5/1

using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string data = "rae*sfe*que(aa+abc)*fed(bb+agh(fd-fg-gh(ty-tu)))*rtd(cc+dfg+fgd+hjk+fgh(vbn/dcv)";

        string regex = @"\(+.*?\)+";

        var matches = Regex.Matches(data, regex, RegexOptions.Multiline);

        foreach(Match item in matches)

        {

            //Console.WriteLine("Full Match: " + item.Groups[0]);

            //Console.WriteLine("Value: " + item.Groups[1]);

        }

        var level0 = Regex.Replace(data, regex, string.Empty);

        //Console.WriteLine(level0);        

        matches = Regex.Matches(level0, @"\w+", RegexOptions.Multiline);

        level0 = "";

        foreach(Match item in matches)

        {

            if(string.IsNullOrEmpty(level0))

            {

                level0 += item.Groups[0];

            }

            else

            {

                level0 += "," + item.Groups[0];

            }

        }       

        Console.WriteLine(level0);

    }

}