Let "x" be a point in "X""n" given by a marking "f" : "R""n" → Γ with a volume-one metric graph structure "L" on Γ. Let "T" be the universal cover of Γ. Thus "T" is a simply connected graph, that is "T" is a topological tree. We can also lift the metric structure "L" to "T" by giving every edge of "T" the same length as the length of its image in Γ. This turns "T" into a metric space ("T","d") which is a real tree. The fundamental group 1(Γ) acts on "T" by covering transformations which are also isometries of ("T","d"), with the quotient space "T"/1(Γ) = Γ. Since the induced homomorphism "f"# is an isomorphism between "F""n" = 1("R""n") and 1(Γ), we also obtain an isometric action of "F""n" on "T" with "T"/"F""n" = Γ. This action is free and discrete. Since Γ is a finite connected graph with no degree-one vertices, this action is also "minimal", meaning that "T" has no proper "F""n"-invariant subtrees.