specify a root in igraph minimum-spanning-tree

Question

[mk]

I have a weighted adjacency matrix and I need to create a directed MST. The problem is that I know the edge weights and the root, so I can generate an MST on an undirected graph, but I cant find a way to then specify a root. If I could specify a root, this would automatically induce directions on all the edges of the MST, completing the task.

Here is some R code:

my_graph <- igraph::graph_from_adjacency_matrix(adjmatrix = cluster_adj_matrix,
                                                   mode = "upper",weighted = TRUE)
my_mst <- igraph::mst(my_graph)                                                   

<next,  add a root>