Bruhat-Tits building of SL(2)

Following Bill Casselman's notes, I will discuss how points in the affine Grassmannian for SL(2) and over a p-adic field (up to equivalence) can be thought of as nodes on an infinite tree. This is a special case of the Bruhat-Tits building of a reductive group over a local field. We will use theory of modules over a DVR. The material are rather elementary and accessible to graduate students.