WPF Combobox editor style binding is not working

Question

I have the following xaml code.

I am trying to bind custom class UnitCategory to combo box.

But seems to be there is an issue in code.

<Grid>  
    <Grid.Resources>  
        <local:ComboSourceConverter x:Key="cscconv" />  
  
        <Style x:Key="UnitCategoryStyle" TargetType="{x:Type igEditors:XamComboEditor}">  
            <Setter Property="ItemsSource" Value="{Binding Path=DataContext.UnitCategories, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Window}}}" />  
            <Setter Property="SelectedItem" Value ="{Binding Path=DataItem.UnitCategory}" />  
            <Setter Property="DisplayMemberPath" Value="Name" />  
        </Style>  
          
        <Style x:Key="UnitStyle" TargetType="{x:Type igEditors:XamComboEditor }">  
            <Setter Property="ItemsSource" Value="{Binding Path=DataItem.UnitCategory, Converter={StaticResource cscconv}}" />  
        </Style>  
  
    </Grid.Resources>  
    <igWPF:XamDataGrid DataSource="{Binding data}" CellChanged="XamDataGrid_CellChanged">  
        <igWPF:XamDataGrid.FieldLayoutSettings>  
            <igWPF:FieldLayoutSettings AutoGenerateFields="False" />  
        </igWPF:XamDataGrid.FieldLayoutSettings>  
        <igWPF:XamDataGrid.FieldLayouts>  
            <igWPF:FieldLayout>  
                <igWPF:FieldLayout.Fields>  
                    <igWPF:Field Name="Item"></igWPF:Field>  
                    <igWPF:Field Name="UnitCategory">  
                        <igWPF:Field.Settings>  
                            <igWPF:FieldSettings EditorStyle="{StaticResource UnitCategoryStyle}" />  
                        </igWPF:Field.Settings>  
                    </igWPF:Field>  
                    <igWPF:Field Name="Unit">  
                        <igWPF:Field.Settings>  
                            <igWPF:FieldSettings EditorStyle="{StaticResource UnitStyle}" />  
                        </igWPF:Field.Settings>  
                    </igWPF:Field>  
                </igWPF:FieldLayout.Fields>  
            </igWPF:FieldLayout>  
        </igWPF:XamDataGrid.FieldLayouts>  
    </igWPF:XamDataGrid>  
</Grid>  

Following view model. Here Unit category is not binding. Drop down in combo box is not showing. Is there any binding issue?

 public class ViewModel : INotifyPropertyChanged  
{  
    public ObservableCollection<DataModel> data { get; set; }  
    public List<UnitCategory> UnitCategories { get; set; }  
    public static List<string> WeightUnits { get; set; }  
    public static List<string> DistanceUnits { get; set; }  
  
    public ViewModel()  
    {  
        this.data = new ObservableCollection<DataModel>();  
  
        this.UnitCategories = new List<UnitCategory>();  
  
        UnitCategory u1 = new UnitCategory();  
        u1.Name = "Wt";  
  
        UnitCategory u2 = new UnitCategory();  
        u2.Name = "Dt";  
  
  
        this.UnitCategories.Add(u1);  
        this.UnitCategories.Add(u2);  
  
  
  
        WeightUnits = new List<string>()  
        {  
            "mg",  
            "g",  
            "kg"  
        };  
  
        DistanceUnits = new List<string>()  
        {  
            "cm",  
            "m",  
            "km"  
        };  
  
        DataModel data1 = new DataModel();  
        data1.Item = "Item 1";  
        
        DataModel data2 = new DataModel();  
        data2.Item = "Item 2";  
   
        this.data.Add(data1);  
        this.data.Add(data2);  
    }  
  
    public event PropertyChangedEventHandler PropertyChanged;  
    protected void OnPropertyChanged([CallerMemberName] string propertyName = "")  
    {  
        if (PropertyChanged != null)  
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));  
    }  
}  
  
public class DataModel   
{  
    public string Item { get; set; }  
    public UnitCategory UnitCategory { get; set; }  
    public string Unit { get; set; }  
  
    public DataModel()  
    {  
    }  
}  
  
public class UnitCategory  
{  
    public string Name { get; set; }  
}