WPF : how to release collection data?

Question

My wpf application memory getting bigger and bigger when I keep use it.

so I want to create a simple one to see if it will release memory:

1. create a wpf project
2. put a ListBox bound collection and 2 Buttons for Load & clear data
3. create an model Person
4. create an observableCollection
5. Load command is load 100,000 persons in to collection
6. Clear command call ObservableCollection.Clear() method.
7. check memory while these steps

XAML:

<DockPanel>
    <UniformGrid Rows="1" Columns="2" DockPanel.Dock="Bottom">
        <Button Content="Load" Padding="0,12" Command="{Binding LoadCommand}"/>
        <Button Content="Clear" Padding="0,12" Command="{Binding ClearCommand}"/>
    </UniformGrid>
    <ListBox ItemsSource="{Binding Persons}"/>
</DockPanel>

Person Model:

public class PersonModel : BindableBase
{
    private int _id = 0;
    public int ID { get { return _id; } set { SetProperty(ref _id, value); } }

    private string _name = string.Empty;
    public string Name { get { return _name; } set { SetProperty(ref _name, value); } }

    public override string ToString()
    {
        return $"{ID:00000} : {Name}";
    }
}

ViewModel:

public MainViewModel()
{
    Persons = new ObservableCollection<PersonModel>();
    Persons.CollectionChanged += (s, e) => {
        LoadCommand.RaiseCanExecuteChanged();
        ClearCommand.RaiseCanExecuteChanged();
    };
}

public ObservableCollection<PersonModel> Persons { get; private set; }

private BindableCommand _loadCommand = null;
public BindableCommand LoadCommand { get { return _loadCommand ?? (_loadCommand = new BindableCommand(LoadExecute, LoadCanExecute)); } }

private BindableCommand _clearCommand = null;
public BindableCommand ClearCommand { get { return _clearCommand ?? (_clearCommand = new BindableCommand(ClearExecute, ClearCanExecute)); } }

private void LoadExecute()
{
    if (!LoadCanExecute())
        return;

    for (int i = 0; i < 1000000; i++)
    {
        Persons.Add(new PersonModel { ID = i, Name = "The quick brown fox jumps over a lazy dog." });
    }
}
private bool LoadCanExecute()
{
    if (Persons.Count > 0)
       return false;

    return true;
}

private void ClearExecute()
{
    if (!ClearCanExecute())
        return;

    Persons.Clear();
}

private bool ClearCanExecute()
{
    if (Persons.Count == 0)
        return false;
    return true;
}

when I start the program(release version), memory usage in Task Manager is about 10mb(Test12.exe process)

when I click load button, memory raise to about 40mb:

but when I click Clear button, memory not trying to go back start size(10mb), but just stay in 39mb, I wait for 10 minutes it won't come down.

So my question is: how to release memory in WPF correctly?