Unique Tree of Order 2

Theorem
There exists exactly one tree of order $2$:


 * Tree-Order-2.png

Proof
By definition, a graph of order $2$ has exactly $2$ nodes.

By Finite Connected Graph is Tree iff Size is One Less than Order, such a tree has one edge.

There is trivially only one way to connect $2$ nodes with one edge.

Hence the result.