Fine-tuning branch indicator

[m3g1dd]

In general, branch indicators behave like this:

I'd like to further fine-tune images inside my branch indicator by TreeViewStyle like this:

TreeView {
    ...
    style: TreeViewStyle {
        indentation: 25
        branchDelegate: Item {
            visible: true // ** visible
            width: 20
            height: 10
            Image {
                // I want this image to be visible only if item has children:
                visible: styleData.hasChildren
                width: 10
                height: 10
                ...
                source: "images/arrow.png"
                transform: Rotation {
                    origin.x: 10 / 2
                    origin.y: 10 / 2
                    angle: styleData.isExpanded ? 0 : -90
                }
            }
            Image {
                // I want this image to be always visible:
                visible: true
                width: 10
                height: 10
                ...
            }
        }
    }
    ...
}

My above visibility setup is NOT taking effect. Am I missing something?