Normally, only parent collections appear by default on the public /collections browse pages with Collection Tree plugin.
But even child collections appear in my v2.2.2 installation : http://data.msh-vdl.fr/CMS/omeka_mame_maj2015/collections/browse
(for instance, Série 11, no 1130 is a child collection).
I suppose it is because I have entered collections directly in the SQL database.
Can someone tell me where I have to intervene in order to modify this behaviour ?