P.S. The tree data structure and voxel volumes primarily reside in host RAM (CPU side) where changes are made. The tree data structure and voxel volumes are also maintained / updated in buffers (parallel arrays) on the GPU RAM where the ray marching is done. The tree data structure on both CPU and GPU side consists of an array of tree nodes and an array of voxel volumes with nodes and volumes being indexed by offsets into said arrays (rather than pointers which GLSL does not support).