Because plotbunnies come not as single spies but in battalions.
Was about to put this under "The Avengers" rather than "Thor," but it is a Thor/Loki piece and focuses on Asgardian crap as much as the Avengers, but they'll be in this story too so yay. This does mean that there will be Avengers spoilers for those of you who have yet to see it. Hope you enjoy.
Warning!: This story features evil!Odin.

Child of Yggdrasil

For all their power, the Aesir were bound to Asgard. They were gods and yet they could be slain, could be overpowered by the dark that crept between and beyond the branches of Yggdrasil.

Odin, King of the Gods and most powerful, sought to rectify this.

Through ritual and union with the Earth goddess Gaea was Odin's son born, and all of Yggdrasil rejoiced.

Were any being in all the realms capable of perfection, it was the Odinson. Like a star he shone, and Odin knew that this child was destined for power and greatness beyond even the All-Father's imaginings. With such power came a price, for as the child grew into his destiny, so would Odin All-Father wane. One day, his own son would overcome him, take his throne and power, and outshine his father in all things.

It was then Odin knew fear.

Again he laid down the rituals and placed his newborn son upon the alter. The babe laughed, already placing trust in his father despite the strangeness, and he did not cry until he saw the blade, as though he knew what was about to happen.

Odin cleaved the babe in two, straight down the middle.

Yggdrasil wept.

When he returned to Asgard, it was with two sons under his arms, light and dark. His wife Frigga met him at the gates, and he could see in her eyes that she knew what he'd done.

"All will be well," Odin said to her, "I split them evenly."

"No," Frigga reached out and touched the soft hair of the fairer child, sleeping peacefully, "The pieces may be even, but the heart lay on this side."

"It matters not."

Frigga knew otherwise. As Odin handed her the second, darker babe, she placed her hand upon his little chest. Indeed there was a heart there now, but it was a false one, forged of his own flesh when he'd been separated from his other half. It was made from himself, and so the boy could only ever love himself, all the while yearning for that which had been taken from him.

The first child who carried the heart would be all the stronger for it, and yet still incomplete. He too would forever be drawn to the second half, but as the stronger he would never know why and reject such urges, for the heart would give him the illusion of completion.

Odin had not erred. He'd ensure that his son now two would remain dependant upon each other without the harmony that would mean their union. The sons of his line were powerful, free to the universe and unbound by Asgard.

And they were his to control.

It had all nearly come undone. When Odin wished to pass on his title to Thor, the stronger of the two halves, he hadn't expected the lengths Loki would go in retaliation.

The second half had always been too clever, but parts of the whole his sons were, and if Thor was the strength and nobility, so Loki was the intellect and the creative. Loki was always asking why and how, and Odin was happy to oblige with answers, for what good was power controlled if stunted?

The boy thought too much, wondered too much as he lie in his bed at night, hands clutching at his chest as if he could dig out the hurt and emptiness that plagued his artificial heart. He questioned, and Odin knew one day that question would be the one to undo all his work, and then Loki would have to be dealt with. He was becoming more unruly as the years went by anyway, harder to control.

But when the day came, it was Loki himself who lay the alternative at Odin's feet. How fortunate that Odin's Jotun heritage chose to manifest itself in his second son on Jotunheim, and similarly reacted to the Casket. Loki was a shape-shifter, and therefore sensitive to such things, but the boy reached an entirely different conclusion.

"The Casket wasn't the only thing you took from Jotunheim that day, was it?"

Odin was caught off guard by the question. He nearly laughed aloud, for clever his son was so very wrong and provided his father with the perfect lie.

"No," he said, his voice grave. And so he built the lie, that his second son was a foundling, abandoned by monsters but loved by his godly family. Odin hoped Loki, in the face of a ruptured life, would cling to him, to cease his wanderings and return to his father's complete control, like his so very loyal brother.

Loki instead became enraged. The lie that he'd lost had been replaced by an even greater lie he believed, and his fury on the matter again only made Odin want to laugh.

Why indeed was Loki not his favorite son? He'd always been so amusing.

The Odinsleep beckoned, and in relief and mirth, Odin gladly slid into it.

When he woke next, he found that his delightful second son had done all the work for him.

Once again, Odin held his son now two as they dangled off the broken bridge. Thor first, as always, who held Gungnir with Loki hanging off its end, his feet in the aether.

"I could have done it, Father! I could have done it! For you, for all of us!"

How easy it would be, to tell his son he understood, to soothe his twisted mind until he could be pulled to safety and then dealt with. But no, even now Loki was too unpredictable, unruly and difficult to control.

He had to be broken first.

"No, Loki."

Disbelief, hurt, and a horrible finality flashed through his son's eyes before his face settled, briefly, into a blank stare that Odin could read all too easily.

Fine.

What comes next is your doing.

Loki let go, despite his other half's pleads, and fell from Asgard into realms unknown.

"No," Odin said, What comes next will be your undoing.

Loki would become stronger on his own, or he would be destroyed. Regardless, Loki would come back, most likely by the hand of his brother who would not be able to do anything but search for him, for they were one.

And with Loki's crimes behind him and word of his 'true' heritage come to light, Odin could break him to his will as he wished in the name of justice.

He pulled Thor back to the safety of the bridge and embraced him, his relief at his first son's safety genuine. Burying his face in his father's shoulder in sorrow, Thor did not see the smile that crept over his father's features.

Loki would come back to him.

Odin needed only to wait.