In Norse Mythology the Ash-Tree is seen as the "World Tree', although it is named as 'Needle-Ash' which some see as being a Yew-Tree. Of course, there are other variants such as the Oak and Birch, and all of these have been used to symbolise the Cosmic Centre. Why did the English Initiates split the Ansuz-Rune into two different runes - Os and AEsc?
The Os-Rune shape is that of a posture used in ancient times to denote a god, and also kingship; this posture was that of a god-king figure holding a Rod and Ring, the arms being in this runic position. The most famous being that of the figure of the Persian Ahura-Mazda, but also other god-figures were shown in this posture. As the 'Rune of Woden' this fits the meaning to this particular rune.
The AEsc-Rune we can see as the Ancestral Rune since 'Ask' was the First Man; with Woden being the Ancestral God we can see the link between these two runes. The Ansuz-Rune would incorporate both meanings in the same rune-stave.
There is a vital clue in the Old English Rune Poem as to how the English Initiates saw the World Tree as an Ash-Tree, and this is found in the AEsc-Rune. In the poem there is reference to - stith on stapule stede rihte hylt - where the term stapule referred to a pillar or post. Here we find what may be a hidden reference to the Ash-Tree as the 'World Pillar' or Irminsul. The clue also lies in the last sentence - deah him feotan on firas monige - 'though many men fight against it', which makes no sense unless we see the World Pillar as being symbolic of World Order which is (like Iggdrasil) continually assailed by the enemies of Truth and Order.
As far as I know no-one has questioned as to why 'many men fight against it' in regard to what they see as an ash-tree in the woodlands. The poem refers to a specific Ash-Tree - Iggdrasil - which is assailed by Dark Forces of Chaos and Evil who seek to overthrow the World Order-Cosmic Order. This is eldum dyre ('dear to men') because it is symbolic of the World Order, but also because the White Tree represents the White Race at one level, very dear to those who belong to it (at that time). The use of the term 'eldum' is significant since it infers that the meaning is not just 'men' but 'men of eld-time'.
Thus, the term stapule is used for a 'Sacred Pillar' or 'Sacred Tree', and not just a pole or post; until Ragnarok this World Pillar stays steadfast and true, but in time it begins to totter under the assault of the Forces of Chaos and Darkness, but it will be regenerated with the cleansing Fire of Surt. So it would seem that the Anglo-Saxons knew the Ash-Tree as the World Tree, and we can see this to be the Ancestral Tree at another level, where the First Man was named 'Ash'. Thus why the AEsc-Rune is the Ancestral Rune.