I've been using non-OOP languages (Mostly scripting or web development) such as Lua for a prety long time. I'm becoming quite advanced in C# now, but I've hit a rock as far as my current project is concerned.

I'm making a sort of game where you make a 2D environment out of various types of things.

I'm using an example I found on the web of porting XNA into a winform, and it works perfectly, no lag or anything.

But that's not my problem. I have absolutely NO IDEA how to make an instanced class communicate with another instanced class that the instanced class didn't instance.

Basically, I've made an "Insert" interface with a button to insert a peice of terrain, which then is meant to apear in Treeview1. How can I tell the form to "reply" that the user has picked the terrain (I'm using an enum for what they picked), and tell the form to add a node to the treeview?