my %hash = ('one' => 1,
	    'two' => {'one' => 1,
		      'two' => {'one' => 1,
			        'two' => 2,
			        'three' => 3}},
	    'three' => 1);

##</code><code>##

if ((keys %{$hash{'one'}})) {
    print "Yes\n";
}
else {
    print "No\n";
}