ok here's what I understood (might be interesting for others), correct me if I'm wrong ...
- The tree is defined by the leaves each branch can have: each branch of the tree has
num_children - First the chunks are summarized by groups of
num_children - The bottom - 1 level is made of
number_of_chunks / num_children (rounded up) branches containing a summary and each branch has num_children leaves/children_chunks - Each of the branches (summaries) in bottom-1 level are now considered as "chunks" and recursion occurs: branches are grouped by
num_children and we go back to step 2 and the whole process repeat until there's nothing to summarize anymore ...
with num_children = 3, here's an example
-root summary
+-- super-summary 1
| +--summary 1
| | +--chunk 1
| | +--chunk 2
| | \--chunk 3
| +--summary 2
| | +--chunk 4
| | +--chunk 5
| | \--chunk 6
| +--summary 3
| +--chunk 7
| +--chunk 8
| \--chunk 9
+-- super-summary 2
+--summary 4
| +--chunk 10
| +--chunk 11
| \--chunk 12
+--summary 5
| +--chunk 13
| +--chunk 14
| \--chunk 15
+--summary 6
+--chunk 16
\--chunk 17