public class AddMonthlyExpenses extends AppCompatActivity {

    ArrayList<ListObj> groupList= new ArrayList<ListObj>();;
    List<String> childList;
    Map<ListObj, List<String>> laptopCollection;
    ExpandableListView listview;
    ExpandableListAdapter expListAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.add_monthly_expenses);
        laptopCollection = new LinkedHashMap<ListObj, List<String>>();
        listview = (ExpandableListView) findViewById(R.id.exlistView);
        expListAdapter = new ExpandableListAdapter(getApplication(), groupList, laptopCollection);
        listview.setAdapter(expListAdapter);
        retrieveList(name);
    }

 public void retrieveList(String name) {
        database = mdb.getReadableDatabase();
        Cursor cursor = database.rawQuery("SELECT * FROM " + MyDatabaseHelper.TABLE__TASK + " WHERE Name = ? ", new String[]{name}, null);
        if (cursor != null && cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                groupList = new ArrayList<ListObj>();
                int iD = cursor.getInt(cursor.getColumnIndex("ID"));
                String month = cursor.getString(cursor.getColumnIndex("Month"));
                double budget = cursor.getDouble(cursor.getColumnIndex("Budget"));
                groupList.add(new ListObj(iD,month,budget));
                createCollection();  // for child items
                if (expListAdapter != null) {
                    expListAdapter.add(iD, month, budget);
                    listview.setAdapter(expListAdapter);
                }
            }
        }
    }

 private void createCollection() {
        String[] options = {"Edit","Delete"};
        for (ListObj laptop : groupList) {
            loadChild(options);
            laptopCollection.put(laptop, childList);
        }
    }

    private void loadChild(String[] laptopModels) {
        childList = new ArrayList<String>();
        for (String model : laptopModels)
            childList.add(model);
    }
}

public class ExpandableListAdapter extends BaseExpandableListAdapter {

    private Context context;
    Map<ListObj, List<String>> laptopCollections;
    private ArrayList<ListObj> laptops;
    private LayoutInflater mInflater;

    public ExpandableListAdapter(Context context, ArrayList<ListObj>laptops, Map<ListObj, List<String>> laptopCollections) {
        this.context = context;
        this.laptopCollections = laptopCollections;
        this.laptops = laptops;
        mInflater = LayoutInflater.from(context);
    }

    public Object getChild(int groupPosition, int childPosition) {
        return laptopCollections.get(laptops.get(groupPosition)).get(childPosition);
    }

    public void add(int id, String month, double budget) {
        String[] splited = month.split("\s+");
        ListObj obj = new ListObj(id, month, budget);
        obj.setYear(splited[1]);
        obj.setMonth(splited[0]);
        obj.setBudget(budget);
        obj.setID(id);
        laptops.add(obj);
        this.notifyDataSetChanged();
    }

    public int getChildrenCount(int groupPosition) {
            return laptopCollections.get(laptops.get(groupPosition)).size();
    }

    public Object getGroup(int groupPosition) {
        return laptops.get(groupPosition);
    }

    public int getGroupCount() {
        return this.laptops.size();
    }

    public long getGroupId(int groupPosition) {
        return groupPosition;
    }
}