MainWindow.xaml

<syncfusion:RibbonWindow x:Class="LoadSpreadsheetControl_InsideStackPanel.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:LoadSpreadsheetControl_InsideStackPanel"
        xmlns:syncfusion="http://schemas.syncfusion.com/wpf"                 
        mc:Ignorable="d"
        Title="MainWindow" Height="650" Width="800">

    <StackPanel>
        <Grid Height="750" Width="1000">
            <Grid.RowDefinitions>
                <RowDefinition Height="70"/>
                <RowDefinition Height="auto"/>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
            <Button Content="Load" Grid.Row="0" VerticalAlignment="Top" Width="100" Click="Button_Click" HorizontalAlignment="Left" Margin="10"/>
            <syncfusion:SfSpreadsheetRibbon Grid.Row="1" syncfusion:SkinStorage.VisualStyle="office2010lBlue"/>
            <syncfusion:SfSpreadsheet Name="spreadsheet" Grid.Row="2" Visibility="Hidden"/>
        </Grid>
    </StackPanel>
</syncfusion:RibbonWindow>