put back the is_tree attributes which where wrong (but unused) but required

5 jobs for master in 61 minutes and 7 seconds (queued for 3 seconds)
Name Stage Failure
failed
pages Deploy
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Preparing to unpack .../tree_1.8.0-1_amd64.deb ...
Unpacking tree (1.8.0-1) ...
Setting up tree (1.8.0-1) ...
$ mkdir .public
$ cp -rf expe/results_expe-current .public/
cp: cannot stat 'expe/results_expe-current': No such file or directory
Cleaning up file based variables
ERROR: Job failed: exit code 1