Flamegraphs are a really lovely tool for visualizing trees. Slightly related anecdote:

A while ago I was experimenting with interactive exploration of (huge) Monte Carlo Tree Search trees. Inspired by file system visualization tools, my first attempts were also tree maps and sunburst graphs, but I ran into the same problems as in the article.

I tried flamegraphs next with the following setup:

- The number of visits in each node maps to the width and order of each bar (i.e., the most visited node was first and was the largest)

- The expected value maps to the color of each bar.

And then it was a perfect fit: it's easy to see what's going on in each branch at the first levels, and the deeper levels can be explored through drilling down.