igraph: tree graph where terminal (not root) nodes are at same level?

I would like to plot a tree graph with igraph in R, having all the terminal nodes at the same level, unlike the default where all root nodes are at the same level.

layout_as_tree has a way to do this, based on the root nodes. One needs to specify them (root), as well as their level (rootlevel). So I could use this option, though it seem it would involve a very complicated workflow of a) splitting my tree into subtrees b) finding the root node of each subtree c) finding the largest path of each subtree 4) specifying root first level relative to others...

Is there a simpler way to do so by starting from the terminal nodes? Say I don't know which nodes are the root ones (1 and 11), but only know which ones are the terminal ones (5:11 and 18:20).

library(igraph)
tree2 <- make_tree(10, 3) + make_tree(10, 2)

plot(tree2, layout=layout_as_tree(tree2, root=c(1,11),
                                  rootlevel=c(2, 1)))

^{Created on 2022-09-23 with reprex v2.0.2}