Find a duplicate in a list and create unique map keys

duplicateProcess.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import javafx.util.Pair;

List<Pair<String,String>> pairList = new ArrayList<>();

pairList.add(new Pair("alpha","100"));
pairList.add(new Pair("alpha","200"));
pairList.add(new Pair("alpha","300"));
pairList.add(new Pair("beta","101"));
pairList.add(new Pair("beta","102"));
pairList.add(new Pair("gamma","1000"));



List<String> duplicateKeys = pairList.stream().collect(Collectors.groupingBy(Pair::getKey))
    .entrySet().stream().filter(list -> list.getValue().size() > 1)
    .map(Map.Entry::getKey)
    .collect(Collectors.toList());

HashMap<String,Integer> counterMap = new HashMap<>();
        duplicateKeys.forEach(k -> {
            counterMap.put(k, 1);
        }) ;
   
        Map<String, Object> options = new TreeMap<>();
        
        pairList.forEach(p -> {
            if (counterMap.keySet().contains(p.getKey())) {
                int ct = counterMap.get(p.getKey());
                String v = p.getValue();
                String k = p.getKey()+ " ("+ct+")";
                ct = ct + 1;
                counterMap.put(p.getKey(),ct);
                options.put(k, v);              
            }
            else {
                options.put(p.getKey(), p.getValue());
            }          
        });

// options now contains    key: 'Alpha (1)' value: 100