This is the solution:
WITH MEMBER [Measures].[Test] AS 0 SELECT { [Test] } ON 0, NON EMPTY { filter ( {[dim user].[userhierarchy].[userlevel1].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel2].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel3].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel4].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel5].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel6].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel7].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel8].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel9].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ), filter ( {[dim user].[userhierarchy].[userlevel10].allmembers } ,[dim user].[userhierarchy].currentmember.children.count > 1 ) } ON 1 FROM [Activities]
I am not filtering by parent user types, but bringing up those users which have the children count greater than 1.