The way to show home as up in fragment when we have items in backstack and hide it when there are not. This snipet should be placed in your MainActivity.

HomeAsUpFragment.java

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(savedInstanceState == null){
            openFragment(MainFragment.newInstance(),false);
        }

        getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                boolean showAsUp = getSupportFragmentManager().getBackStackEntryCount()>0;
                getSupportActionBar().setDisplayHomeAsUpEnabled(showAsUp);
            }
        });
    }

    @Override
    public boolean onSupportNavigateUp() {
        getSupportFragmentManager().popBackStack();
        return true;
    }