C中指针的奇怪分段错误

I should be doing a program that builds a tree from an existing array, with some property. My issue is not about how doing that (I should be doing some recursive fuctions, and it's ok), since when I tried to launch the building function I had some segmentation fault. So I tried to "isolate" the problem and I saw that I had it when I created the root node of the tree. I really couldn't understand why I had that error (since I've been using lists for a while, so, even if I'm not a guru, I'm not completely new in pointers and linked structures neither). I tried to write a very simple main code for seeing what was happening, and I saw that I couldn't even initialize a single node. Here is the code:I should be doing a program that builds a tree