private func hierarchySize(hierarchy: Hierarchy<String>) -> CGSize {
    let firstSize = textSize(hierarchy.value)
    var maxWidth = firstSize.width
    var sumOfHeights = firstSize.height
    for child in hierarchy.children {
        let childSize = hierarchySize(hierarchy: child)
        maxWidth = max(maxWidth, indentSize + childSize.width)
        sumOfHeights += rowSpacing + childSize.height
    }
    return CGSize(width: maxWidth, height: sumOfHeights)
}