>>715502725
Miquella's Haligtree was never about his ascension per say, it was about creating a new Erdtree, which Marika actually signed off on. He watered the tree with his own body and blood, but the ritual couldn't be completed.

There are also clues to the making of the great trees in Nightreign through the sacrificial maidens of the cutting-gifted tribe creating a spirit tree.

Miquella intended to ascend with Radahn regardless, but getting captured by Mohg was never necessarily the plan. Radahn's only cost to Miquella's request was to be defeated in combat—it was essentially how Miquellla would "earn" Radahn's favor, so Miquella sent Malenia to do the deed. The whole plan got botched through Malenia's defeat. However, he likely intended for Mohg to be the sacrifice for Radahn's rebirth after Radahn made his request.

When Miquella was ready to journey through the Land of Shadow, he sent for his charmed knights—Leda most of all—and they were tasked with eliminating Mogh. However, the Tarnished beat her to it.

The DLC actually made it clear that everything Miquella did was in effort to be contrary to his mother, though he was the most favored of Marika anyways. Though it only proved that Miquella was more like Marika than any of her other children, and he was walking down the same dark path Marika took to ascenscion—though Miquella's journey was literally a metaphysical discarding of demigod aspects, it mirrored Marika's journey of discarding her emotions, her empathy, her love, and all that made her human—that's why godhood is a prison.

So yeah, it's incredibly easy to understand.