Define Style of DataGridTextColumn tooltip - wpf

Question

I am trying to change the style of the tooltip of DataGridTextColumn, But the xaml code below doesn't work. When I run the application, custom tooltip is shown and System.Windows.Style is written in it. The button isn't shown too. Where do I have mistake?
<DataGrid.Columns>
<DataGridTextColumn Width="*" Binding="{Binding W_NAME}" Header="Name">
<DataGridTextColumn.CellStyle>
<Style TargetType="DataGridCell">
<Setter Property="ToolTip">
<Setter.Value>
<Style TargetType="ToolTip">
<Setter Property="OverridesDefaultStyle" Value="True"/>
<Setter Property="HasDropShadow" Value="True"/>
<Setter Property="HorizontalAlignment" Value="Left"/>
<Setter Property="Content" Value="mytext"/>
<Setter Property="VerticalAlignment" Value="Center"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ToolTip">
<Border Name="RootElement" CornerRadius="2,2,0,0">
<Border.Background>
<SolidColorBrush x:Name="BorderBrush" Color="Black"/>
</Border.Background>
<Grid Margin="4" Background="{TemplateBinding Background}">
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
VerticalAlignment="{TemplateBinding VerticalAlignment}"
TextElement.FontFamily="{DynamicResource Glaho}"
Content="{TemplateBinding Content}"
Margin="4,5,4,4">
</ContentPresenter>
<Button Content="This is button" HorizontalAlignment="Right" Command="{Binding somecommand}"/>
</Grid>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
</Style>
</DataGridTextColumn.CellStyle>
</DataGridTextColumn>

Answer 1

You're very close, the problem is you've set the Style as the ToolTip itself:
<Style TargetType="DataGridCell">
<Setter Property="ToolTip">
<Setter.Value>
<Style TargetType="ToolTip"> <-------------- badness!
What you need to do is set a ToolTip control as the ToolTip, and then set the Style on that:
<Style TargetType="DataGridCell">
<Setter Property="ToolTip">
<Setter.Value>
<ToolTip>
<ToolTip.Style>
<Style TargetType="ToolTip">