Back button is Not working in actionBar

By pressing actionBar icon I should go to previous Fragment but it is not going. I mean nothing happen when I press actionbar icon.

public class SecFrag extends Fragment {

// constructor and onCreateView goes here

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Toolbar toolbar = (Toolbar)getActivity().findViewById(R.id.toolbar);
        ((AppCompatActivity)getActivity()).setSupportActionBar(toolbar);
        ActionBar actionBar=((AppCompatActivity)     getActivity()).getSupportActionBar();
        actionBar.setDisplayShowHomeEnabled(true);
        actionBar.setDisplayHomeAsUpEnabled(true);
        actionBar.setHomeButtonEnabled(true);


        recyclerView= (RecyclerView) getActivity().findViewById(R.id.recyclerViewInSecFragment);
        RecyclerAdapter adapter=new RecyclerAdapter(MainActivity.musicList,null,null);
        recyclerView.setAdapter(adapter);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        Log.e("SEC",item.getItemId()+"");
        switch (item.getItemId())
        {
            case android.R.id.home:
            {
                Log.e("SECFRAG","CLICKED");
                break;
            }
           default:break;
        }
        return super.onOptionsItemSelected(item);
    }
}

So it's not going to trigger android.R.id.home in the switch statement. So please suggest why this is not working.