Hi,
what do you mean by custom techtree? Are you playing Crusade or the main Game? In crusade, there is no custom techtree for factions. Unless you create a faction unique trait. In this case you also need the line;
<RaceTrait>
<Option>*faction unique trait*</Option>
</RaceTrait>
under <Techs> in your <Prerequ>
plus, you have to add this trait to your faction.