DataGrid sorting doesn't work
<p>I have a <code>TabControl</code> that has one <code>TabItem</code>with a <code>DataGrid</code> inside.</p>

<pre><code>&lt;TabControl Background="{DynamicResource StandardBackgroundColor}" 
            Grid.Row="2" Grid.Column="1"
            BorderBrush="{DynamicResource StandardBorderColor}" 
            DataContext="{Binding ChartViewModel}"&gt;


&lt;TabItem Header="{lex:Loc Data}"&gt;
           &lt;DataGrid Name="TagGrid" ItemsSource="{Binding UnionAllSerie}" 
                     ColumnWidth="*" Background="#CCCCCC"&gt;
                    &lt;DataGrid.Columns&gt;
                        &lt;DataGridTextColumn Header="Name" Binding="{Binding Name}" /&gt;
                        &lt;DataGridTextColumn Header="{lex:Loc time}" SortDirection="Descending"
                                            Binding="{Binding X, Converter={StaticResource OleDateToDateTimeConverter}, StringFormat=\{0:dd/MM/yy HH:mm\}}" /&gt;
                        &lt;DataGridTextColumn Header="{lex:Loc Measure}"
                                            Binding="{Binding Y}" /&gt;
                    &lt;/DataGrid.Columns&gt;
            &lt;/DataGrid&gt;
&lt;/TabItem&gt;
</code></pre>

<p>Where my UnionAllSerie is declared as follow:</p>

<pre><code>public ObservableCollection&lt;Data&gt; UnionAllSerie { get; set; } = new ObservableCollection&lt;Data&gt;();
</code></pre>

<p>This collection of data is populated depending on the action performed on the window. What I want is to have the <code>Grid</code> automatically sorted by the second column, which represents the date.</p>

<p>Does anybody know what I am doing wrong or missing?
Thanks!</p>