The visual tree determines the rendering order of WPF visual and drawing objects. The rendering order of traversal starts with the root visual, which is the top most element in the root visual tree. The root visual’s children are then traversed, left to right. Find the following button control rendering order in visual tree.
Reference link: https://docs.microsoft.com/en-us/dotnet/framework/wpf/graphics-multimedia/wpf-graphics-rendering-overview