Glad you enjoyed the greenhouse!! 😁

Yup, a dirty workaround would be to plot the non ultrametric tree with ggtree. Extract leaves coordinates and add the difference between leaves coordinates and the farthest leaf so that they are all equally far from the root.

Anyway I feel like you have already better answers.
Hope you'll find out

Indeed :D

Got that using log(1+tr$edge.length)
Not quite the same but better

Hi. I suppose their is an option in ggtree and associated packages to do so. A workaround might be to directly log your branch length?
Let's say you used ape to import your tree:

mytree$edge.length <- log(mytree$edge.length)