Insert a node in a binary search tree

The teacher gave us this code that inserts a node in a binary search tree, but I am not sure what the $ z.p = y$ instruction does. wouldn’t the algorithm work without it?

abr_insert(T, z) //z is the node that must be inserted     {             y = NULL;             x = T.root;             while(x != NULL)             {                     y  = x;                     if(z.key < x.key)                             x = x.left;                     else                             x = x.right;             }             z.p = y; //here is the instruction that I don't understand             if(y = NULL)                 T.root = z;             else if(z.key < y,key)                     y.left = z;             else                     y.right = z;     }