Olivier I don't know how a filter could know whether you need only contrats and not the factures... however if you need a quick solution for the following…
I could click on a main task and display only that task and all its subtasks, I would also save a lot of time.
You may always use the GUI to open the details view, select in the Details the same view as in the main (in your case 'Ressource / Budget approuvé'). Then selecting any given item on the main view, shows it and its subtasks in the details view.
To quicken this action, I just wrote a script.
Feel free to install it in your Files > Actions > … to be able to select and run at anytime.
tell application "Merlin Project"
tell window 1
tell configuration
-- show both panes: main and detail
set views splitter state to {collapse state:both views visible}
tell pane 1
-- check title and type of pane 1
set title_pane1 to title of active view
set type_pane1 to active view type
end tell
tell pane 2
-- set type of pane2 to type of pane 1
set active view type to type_pane1
-- select the same view in pane2 as in pane 1
set active view to item 1 of (views whose title is title_pane1)
end tell
end tell
end tell
end tell
