But it's a reticulating structure; yes, the graph is directed / partially ordered, but it's certainly not tree-like.
The key property of real trees is that they _branch_ and the branches don't recombine.
The key property of real trees is that they _branch_ and the branches don't recombine.
I do agree that branches staying separate is the essential property of a tree data structure.
The need to connect leaves to roots is what gives individuals trees their branching nature. Obviously a tree can have holes in it etc, but loops in nutrient delivery present an inherent issue.