Exclude a member of hierarchy

[philelmousse]

Hello,

I have a dimension with that hierarchy of 3 level :

Group
SubGroup
Category

I have a crosstab build with some group members and one category member. The category member that I display is also part of a group member I displayed. I would like exclude that category member of the group to have to good value.
The dimension :

Group1 Subgroup1 Category1
Group1 Subgroup2 Category2
Group2 Subgroup3 Category3

In my crosstab I display :

Group1
Group2
Category2

That mean in the crosstab in group1 row I get the value of Category1 and Category2. How manage that ?