Thanks for the answer Subodh , I have checked the collapse Category (ON) and tried both left and top attributed.. I manage to see the main categories on the left and manage to see a partial of the secondary level but part of it is still hidden under the products... it's as if the product block has priority over the categories...

Check the "Collapse Category Recursive" option under the Products Page properties.  This is below the setting where you define if the Categories should be displayed on Left and/or Top.