When I closed my computer on friday everything was still ok, but when starting Creo this morning my planes are missing from the model tree.
But when I create a new part the planes are visible in the model tree.
you have to save Model Tree configuration into a file and set MDL_TREE_CFG_FILE in config.pro to point to this file.
PLanes are features and assembly tree by default does not show features. Part files do show features.
You can turn features on in assemblies by clicking on the hammer tool at the top of the tree and selecting the top option.