확장 리스트 뷰에서 부모 그룹 클릭시 자식 리스트가 나오잖아요

그런데 이때 자식 리스트를 누르며 또 자식 밑의 자식 리스트가 나오게 하고 싶습니다

이게 가능한가요??

부모1

    자식1

        자식1-1

        자식1-2

        자식1-3

    자식2

    자식3

부모2

부모3

이렇게 하고싶은데 어디를 건들어야될지 모르겠네요...

책의 소스는 이렇게 되있습니다

package com.androidside.expandablelistdemoa1;

import android.app.Activity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.BaseExpandableListAdapter;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.TextView;
import android.widget.Toast;

public class Main extends Activity implements
        ExpandableListView.OnGroupClickListener,
        ExpandableListView.OnChildClickListener{
    ExpandableListView listView;
    String[] groups = { "Number", "Alphabet" };
    String[][] childs = { { "1", "2", "3", "4", "5" },
            { "A", "B", "C", "D", "E" }};

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ExpandableListAdapter listAdapter = new MyExpandableListAdapter();

        listView = (ExpandableListView) findViewById(R.id.listview);
        listView.setAdapter(listAdapter);
        listView.setOnGroupClickListener(this);
        listView.setOnChildClickListener(this);       
    }

    public class MyExpandableListAdapter extends BaseExpandableListAdapter {

        public Object getChild(int groupPosition, int childPosition) {
            return childs[groupPosition][childPosition];
        }

        public long getChildId(int groupPosition, int childPosition) {
            return childPosition;
        }

        public int getChildrenCount(int groupPosition) {
            return childs[groupPosition].length;
        }

        public TextView getGenericView() {
            AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT, 64);

            TextView textView = new TextView(Main.this);
            textView.setLayoutParams(lp);
            textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
            textView.setPadding(36, 0, 0, 0);
            return textView;
        }

        public View getChildView(int groupPosition, int childPosition,
                boolean isLastChild, View convertView, ViewGroup parent) {
            TextView textView = getGenericView();
            textView.setText(getChild(groupPosition, childPosition).toString());
            return textView;
        }

        public Object getGroup(int groupPosition) {
            return groups[groupPosition];
        }

        public int getGroupCount() {
            return groups.length;
        }

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

        public View getGroupView(int groupPosition, boolean isExpanded,
                View convertView, ViewGroup parent) {
            TextView textView = getGenericView();
            textView.setText(getGroup(groupPosition).toString());

            // 그룹 표시 아이콘 존재 여부
            listView.setGroupIndicator(null);

            return textView;
        }

        public boolean isChildSelectable(int groupPosition, int childPosition) {
            return true;
        }

        public boolean hasStableIds() {
            return true;
        }
    }

    public boolean onGroupClick(ExpandableListView parent, View v,
            int groupPosition, long id) {
        Toast.makeText(this, "Group : " + groups[groupPosition], Toast.LENGTH_SHORT).show();
       
        return false;
    }

    public boolean onChildClick(ExpandableListView parent, View v,
            int groupPosition, int childPosition, long id) {
        Toast.makeText(this, "Child : " + childs[groupPosition][childPosition], Toast.LENGTH_SHORT).show();
       
        return true;
    }
}