Button 源自“ContentControl”;这意味着它通过其“.Content”属性支持一个子项;这是它的默认属性。对于您的情况,您可以简单地:
<Button x:Name="CB_AddNode"
Foreground="DarkGreen"
ToolTipService.ToolTip="Add node under selected node.">
<Path Data="M10,4H4C2.89,4 2,4.89 2,6V18A2,2 0 0,0 4,20H20A2,2 0 0,0 22,18V8C22,6.89 21.1,6 20,6H12L10,4Z"
Stretch="Uniform"
Fill="Goldenrod"
Width="20"
Height="20"
Margin="0,0,0,0"
RenderTransformOrigin="0.5,0.5">
<Path.RenderTransform>
<TransformGroup>
<TransformGroup.Children>
<RotateTransform Angle="0" />
<ScaleTransform ScaleX=".8"
ScaleY=".8" />
</TransformGroup.Children>
</TransformGroup>
</Path.RenderTransform>
</Path>
</Button>