In ChessBase 12, when viewing an Opening Tree, why do all the games always stop near move 26?

Question

I have ChessBase 12 64Bit. To create an Opening Tree I do the following steps:

• I click on "Mega Database 2014".
• I filter all the 5.8 millions games like I want (for example, taking only the games where a specific player was White).
• Right click > Edit > Select all.
• Right click > Edit > Clip or unclip.
• File > New > Database > Save as type: Books (*.CTG)
• And then I drag the "Clip Database" to my newly created Opening Tree.
• The newly created Opening Tree works fine.

But there is just one problem: all the games always stop near move 26 (sometimes at move 23, sometimes at move 29).

Why is that? And how can I fix this?

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Edit:

Both of the current answers are completely incorrect.

I had the confirmation from two other independant people that their opening trees in their ChessBase do not stop after a certain number of moves!

They both told me that in order to make an opening tree that doesn't stop after a certain number of moves, we simply had to select "Absolute Length" and then input a big number (100 will work) for the "Length".

See page n°103 of this manual: http://download.chessbase.com/download/pdf/ManualFritz13.pdf

But that's what I have always done, and it doesn't work.

I have tried to input various numbers for the "Length": 5, 10, 15, 20, 30, 40, 50, 100, 200, 400. And surprisingly, no matter what number I put, the opening tree always stop near move 26!

I also tried to pick "ECO-Relative Length" instead of "Absolute Length", and weirdly there was absolutely no difference: the opening tree still stops near move 26.

This means that there really is a big problem, a bug. ChessBase is simply ignoring whether I choose "Absolute Length" or "ECO-Relative Length" and what number I put for the "Length"...

Answer 1

"Move 26" (or thereabouts) is the "midpoint" of most chess games.

Your opening tree application appears to working fine in getting you to the peak or "combustion point" of most games. (That seems to be its purpose.) From there, it's mostly downhill.

Answer 2

well, in terms of chess phase classification, move 20 is really middlegame not an opening, so the tree should be cut somewhere, I think that function should work when you want to see the first 5 or 10 moves of an opening, and then study other main lines, so that is basically a reasonable choice.