Structural theory of trees. I. Branching and condensations of trees

Abstract: Trees are partial orders in which every element has a linearly ordered set of predecessors. Here we initiate the exploration of the structural theory of trees with the study of different notions of \emph{branching in trees} and of \emph{condensed trees}, which are trees in which every node is a branching node. We then introduce and investigate two different constructions of \emph{tree condensations} -- one shrinking, and the other expanding, the tree to a condensed tree.