I couldn't find a better way to describe what I mean, so have a look at these:

It goes from this:

To this:

It is possible with the /fill command, but I couldn't find any other way to do this. Fun fact: after using the/fill command the affected blocks of the tree become "transparent" and you can place blocks in them manually/without commands. Weird... Here:

This issue has gone stale due to inactivity. Please comment again if it is still an issue.

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