ListView, BindingContext, Binding - What am I doing wrong?

Hi everyone.
I'm having hard time to make ListView to show my data.
I hope someone can show me the right path.

I have view model with Items property:

public class MainViewModel
    {
        public ObservableCollection<string> Items= new ObservableCollection<string> { "one", "two", "three", "Four", "Five" };
    }

I have NavigationPage with the BindingContext property set to the view model during instantiation.

var viewModel = new MainViewModel();
var page = new NavigationPage(new TestPage())
            {
                Title = "Test",
                BindingContext = viewModel
            };

Now I want to bind ItemSource property of the ListView to the Items property of the view model passed as a BindingContext of the page like this:

<ListView ItemsSource="{Binding Path=Items}" />

But it seems like it doesn't work that way.

Whenever I set Items directly to BindingContext of the page and then bind ItemSource of the ListView like this:

var viewModel = new MainViewModel();
var page = new NavigationPage(new TestPage())
            {
                Title = "Test",
                BindingContext = viewModel.Items
            };

<ListView ItemsSource="{Binding .}" />

it works.
But I want to set view model once as BindingContext of the page and then bind ItemSource to its property.
What am i doing wrong?