<Window.Resources>
        <ObjectDataProvider x:Key="dataSetProvider"
                            MethodName="CreateDataSet"
                            ObjectType="{x:Type local:DataSetCreator}"></ObjectDataProvider>
        <DataTemplate x:Key="DetailTemplate">
            <TextBlock Text="{Binding UNITNAME}"/>
        </DataTemplate>
        <HierarchicalDataTemplate
            x:Key="MasterTemplate"
            ItemsSource="{Binding Path=UNIT_UNIT}"
            ItemTemplate="{StaticResource DetailTemplate}">
            <TextBlock Text="{Binding UNITNAME}"/>
        </HierarchicalDataTemplate>
    </Window.Resources>

<TreeView Margin="6,39,5,38" Name="unitsTreeView" DataContext="{DynamicResource dataSetProvider}"
                              ItemsSource="{Binding UNIT}"
                              ItemTemplate="{StaticResource MasterTemplate}" SelectedItemChanged="unitsTreeView_SelectedItemChanged" >
                        <TreeView.ItemContainerStyle>
                            <Style>
                                <Setter Property="TreeViewItem.IsExpanded" Value="True"></Setter>
                            </Style>
                        </TreeView.ItemContainerStyle>
                    </TreeView>

class DataSetCreator
    {
        public static DataSet1 CreateDataSet()
        {
            DataSet1 ds = new DataSet1();
            UnitAdapter unitAdapter = new UnitAdapter(Properties.Settings.Default.connectionString);
            DataSet1.UNITDataTable unitTable = unitAdapter.GetAllUnits();
            foreach (DataSet1.UNITRow ur in unitTable.Rows)
            {
                DataSet1.UNITRow newur = (DataSet1.UNITRow)ds.Tables["UNIT"].NewRow();
                newur.ItemArray = ur.ItemArray;
                ds.Tables["UNIT"].Rows.Add(newur);
            }
            ds.Tables["UNIT"].DefaultView.RowFilter = "PARENTNAME = 'Кореневий підрозділ' AND UNITID <> 0";
            return ds;
        }
    }

<HierarchicalDataTemplate
            x:Key="DetailTemplate"
            ItemsSource="{Binding Path=FK_UNIT_UNIT}">
            <TextBlock Text="{Binding UNITNAME}"/>
        </HierarchicalDataTemplate>
        <HierarchicalDataTemplate
            x:Key="MasterTemplate"
            ItemsSource="{Binding Path=FK_UNIT_UNIT}"
            ItemTemplate="{StaticResource DetailTemplate}">
            <TextBlock Text="{Binding UNITNAME}"/>
        </HierarchicalDataTemplate>