public class SessionsFragment extends Fragment {

ExpandableListAdapter expandableListAdapter;
ExpandableListView expandableListView;
List<String> listDataHeader;
HashMap<String, List<String>> listDataChild;
ImageButton addButton;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_sessions, container, false);

    // Get the ListView
    expandableListView = view.findViewById(R.id.sessionsExpandableListView);

    // Prepare the list data
    prepareListData();

    expandableListAdapter = new ExpandableListAdapter(getContext(), listDataHeader, listDataChild);

    // Set the list adapter and expand lists by default
    expandableListView.setAdapter(expandableListAdapter);
    expandableListView.expandGroup(0);

    // Get button values
    addButton = view.findViewById(R.id.addButton);
    addButton.setOnClickListener(new ImageButton.OnClickListener() {
        @Override
        public void onClick(View view) {
            Toast.makeText(getActivity(), "Session added", Toast.LENGTH_SHORT).show();
        }
    });

    return view;
}

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="55dp">

<TextView
    android:id="@+id/listItem"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="16sp"
    android:paddingTop="5dp"
    android:paddingBottom="5dp" />
    <!--android:paddingLeft="?android:attr/expandableListPreferredChildPaddingLeft"/>-->

<ImageButton
    android:id="@+id/addButton"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:src="@drawable/ic_add_black_24dp"
    android:layout_alignParentRight="true" />