I used WPF very little before and some stuff seemed very different to achieve. Coming from a winforms background, what things will seem different and take you a while to figure out.
Off top of my head, I remember not being able to specify which nodes are selected in a treeview control the way it's done in winforms, if I am not wrong.
I remember the whole MVVM principle..
But its okay now.. we are bffs now! :)
For your selected node in a treeview the ModelView ViewModel approach works well. People have worked out good design patterns now for this kind of thing making the process much more easy.
Oh, where to begin? WPF and WinForms seem very different to me. The concept of defining layouts using markup is quite different, although similar to web development. The fact that you need to make an explicit choice of a layout container (for multiple elements) is novel. I remember trying to add a bunch of elements directly within a Window and getting very confused...
I think to take advantage of all that WPF has to offer, you need to have a WPF mindset. For example, you don't have to use styles, templates, and bindings, but those concepts are where the power of WPF lies.
As Daniel stated WPF is different and it needs a different Mindset. You have to forget all the UI side assumptions you made/learned while doing Winforms or other conventional UI side development I have comeacross so many similar kind of questions in this site. Some interesting once are listed bellow. You can find many here.