I am trying to prove the following result from my book:
Let $G$ be a directed graph with vertices $x_1,x_2,\dotsc, x_n$ for which a directed Eulerian circuit exists.
A spanning arborescence with root $x_i$ is a spanning tree $T$ of $G$, with root $x_i$, such that for all $j\ne i$ there is a directed path from $x_j$ to $x_i$ in $T$.
Show that the number of spanning arborescences of $G$ with root $x_i$ does not depend on $i$.
I understand that the sum of all the indegrees must match with the sum of all outdegrees in $G$, for each time we enter a vertex we also leave it. But that's about all I know.
Can someone help me in proving this result?