Menu is not working properly in WPF

<Menu Height="30" Name="menu1" VerticalAlignment="Top" BorderThickness="2"
            Foreground="White" FontSize="16" FontWeight="Bold" Margin="-2,-2,0,0" Grid.RowSpan="2" Grid.ColumnSpan="66">
          <Menu.Background>
              <LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
                  <GradientStop Color="#FF3A60AD" Offset="0.528"/>
                  <GradientStop Color="#FF6A85D8" Offset="0.01"/>
                  <GradientStop Color="#FF3464C4" Offset="1"/>
                  <GradientStop Color="#FF202E7E" Offset="1"/>
              </LinearGradientBrush>
          </Menu.Background>
          <Menu.BitmapEffect>
              <DropShadowBitmapEffect />
          </Menu.BitmapEffect>
          <MenuItem Header="File" IsCheckable="True" Click="MenuItem_Click">
              <MenuItem Header="Open" IsCheckable="true">
                  <MenuItem.ToolTip>
                      <ToolTip>
                          Open a file.
                      </ToolTip>
                  </MenuItem.ToolTip>
              </MenuItem>
              <MenuItem Header="_Close" IsCheckable="true"/>
              <MenuItem Header="_Save" IsCheckable="true"/>

              <Separator/>
              <MenuItem Header="Sub Items">
                  <MenuItem Header="Child1 SubItem" IsCheckable="true"/>
                  <MenuItem Header="Child2 SubItem" IsCheckable="true">
                      <MenuItem Header="GrandChild2 SubItem" IsCheckable="true"/>
                  </MenuItem>
              </MenuItem>

          </MenuItem>
          <MenuItem Header="Settings" IsCheckable="true" Foreground="Orange" FontSize="16" >

          </MenuItem>
          <MenuItem Header="Security" IsCheckable="true" Foreground="White" FontSize="16">

          </MenuItem>
          <MenuItem Header="Database" IsCheckable="true" Foreground="LightGreen" FontSize="16">


          </MenuItem>
      </Menu>