THE ELTBOOKS SIMPLE GUIDE TO THE OXFORD READING TREE

Trunk: Main Stories with Kipper and Friends
The "trunk" of the Oxford Reading Tree is composed of the Main Stories featuring Kipper, Biff, Chip and Floppy the dog. These are sold in packs of 6 for each Stage with 10 Stages. There's a plot that goes through the individual stories and Stages that delights children as they read and get to know more about the characters.

Branches: More Stories with Kipper and Friends
For those who want more to read at each Stage there are many additional stories about Kipper and friends in the More Stories packs (6 books per pack). These don't advance the plot that runs through the Stages but are great to read in their own right.

The Main Stories and More Stories are also sold in specially-priced Trunk Packs and Value Packs and in the Tadoku Pack which includes the 30 packs above (6 books per standard pack, 180 books in total). See below for details.

Roots: Floppy's Phonics, Decode and Develop, Traditional Tales
In addition to the Kipper stories there are also lots of other ORT series such as Traditional Tales (a fully-decodable set of 40 stories sold in packs of 4 books per Stage) and the Decode and Develop stories (sold in packs of 6 books per Stage) which are also phonically decodable.  

Many people suggest a reading order of:

1) Floppy's Phonics 

2) Decode and Develop 

3) the early Stages of Traditional Tales 

before moving on to the Main Stories and More Stories that feature Kipper and friends.

Tree Tops and More
When the "roots", "trunk" and "branches" of Stages 1~9 have been completed, children can move on to TreeTops which provides even richer reading materials. Other branches of ORT include Story Sparks, InFact and more.

For more information about the Oxford Reading Tree, download the explanatory PDF here.