Cannot access Atreus' skill tree?

[onomastikon]

I spent the first couple of XP points I had on buying a skill for Atreus, just to try it out -- since I cannot buy any axe skills, apparently I need to upgrade my axe first (?). Anyhow, just a few more minutes into the game and I cannot even look at the skill tree -- it's greyed out. I have no idea what the skill or skills was or were that I bought, nor can I buy any more. It is inaccessible. Is this a bug? I don't see anything via search engines on it.