Hi
I did use Maxime Herpin 's mtree addon and planted a few trees with it.
Cool stuff.
Then I saved and closed my TestTree file, went to other projects in Blender.
Probably changed some setting … I do not remember which exactly 
Reopening the TestTree file , I do not see existing nodes in ntree node tree window. The tree is still there, I can select it’s objects but the nodes are hiding somewhere.
If I try to add nodes, all options ( trunk, roots …) are greyed.
Same gray for View All same gray for all select options.
Under the Node menu Move, Rotate and Resize are nor greyed but they do not seem to do anything when used.
Same grey behavior when I try to grow a new tree from scratch in a new file.
Any idea ?
Thanks !