I need help grouping words from a list into sublists in C#

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace HangMan
{
    public partial class Form3 : frmNormal
    {
        protected string[] wordbank;
        private int counter = 0;
        //protected ArrayList patterns = new ArrayList();
        List<string> patterns = new List<string>();
        public Form3()
        {
            InitializeComponent();
        }

        private void Form3_Load(object sender, EventArgs e)
        {
            words();
            chooseword();
            generatelist();
        }

        private void generatelist()
        {
            wordbank = new string[allWords.Length];
            for (int i=0; i<allWords.Length; i++)
            {
                if (allWords[i].Length==currentWord.Length)
                {
                    wordbank[counter] = allWords[i];
                    counter++;
                }
            }
        }

        public override void check(char choice, char[] find, char[] temp)
        {
            allpatterns(choice,find,temp);
            groupwords(choice,find,temp);
        }
        public override void btn_Click(object sender, EventArgs e)
        {
            base.btn_Click(sender, e);
        }

        public string pattern(string word, char choice, char[] find, char[] temp)
        {
            if (word.Contains(choice))
            {
                for (int i = 0; i < find.Length; i++)
                {
                    if (find[i] == choice)
                    {
                        temp[i] = choice;

                    }
                }
                copyWord = new string(temp);
                return copyWord;
            }
            else
            {
                return copyWord;
            }
        }
        
        public void allpatterns(char choice, char[] find, char[] temp)
        {
            for (int i=0; i<counter; i++)
            {
                string p = pattern(wordbank[i], choice, find, temp);
                if (patterns.Contains(p))
                    {
                        //do nothing
                    }
                else
                    {
                    patterns.Add(p);
                    }
            }

        }

        public void groupwords (char choice, char[] find, char[] temp)
        {
            /*ArrayList[] groupedwords = new ArrayList[patterns.Count];
            for (int i=0; i<patterns.Count; i++)
            {
                groupedwords[i] = new ArrayList();
            }*/
            List<List<string>> groupedwords = new List<List<string>>();
            //List<string> subgroup = new List<string>();
            for (int i=0; i<patterns.Count; i++)
            {
                groupedwords.Add(new List<string>());
            }
            for (int i=0; i<counter; i++)
            {
                string word = wordbank[i];
                string p = pattern(word, choice, find, temp);
                int index = patterns.IndexOf(p);
                groupedwords[index].Add(word);
            }
            largestlist(groupedwords,choice,find,temp);
        }

        private void largestlist (List<List<string>> groupedwords, char choice, char[] find, char[] temp)
        {
            for (int i=1; i<patterns.Count; i++)
            {
                int size = groupedwords[0].Count();
                int size2 = groupedwords[i].Count();
                if (size<size2)
                {
                    groupedwords[0] = groupedwords[i];
                }
            }
            /*for (int i=0; i<patterns.Count; i++)
            {
                for (int j=0; j<groupedwords[i].Count; j++)
                {
                    groupedwords[i].RemoveAt(j);
                }
                
            }
            int size = groupedwords[0].Count;
            copyWord = "";
            for (int i=0; i<size; i++)
            {
                copyWord += "_";
            }*/
            copyWord = groupedwords[0].ToString();
            display();
            if(!groupedwords[0].Contains(choice.ToString()))
            {
                wrong++;
            }
            result();
            int random = (new Random()).Next(wordbank.Length);
            currentWord = allWords[random];
            allpatterns(choice,find,temp);
            groupwords(choice, find, temp);
        }
    }
}