Nordic religion before Christianity

The idea of a tree giving Odin power. Ragnarok itself. The norse apparently thought it was an insult to be called a woman and Odin thus gets insulted for acquiring "womanly powers" when acquiring his powers. Hanging from a tree for 9 days.

Clearly christianity influenced Norse tales. I have heard it says that some branched of Hinduism had a lot in common with German paganism.

I am very interested in peeling back the layers. I love to see the parts. For example I have heard it said that Hodr and Baldr were part of an older myth about summer. That Lotur was an ancient version of Loki.

My question is, how was nordic religion before Christianity in its many layers. And where can I find more about Indo-European comparative reconstruction of religion where we can see the layers.