godot/core/math/bvh_structs.inc

public …
struct ItemRef { … };

// extra info kept in separate parallel list to the references,
// as this is less used as keeps cache better
struct ItemExtra { … };

// tree leaf
struct TLeaf { … };

// tree node
struct TNode { … };

// instead of using linked list we maintain
// item references (for quick lookup)
PooledList … }