You summon the yggdrasil, the tree of the nine worlds, which is at your command for a year, if you concentrate enough.
   The tree itself is a cylinder with a 60ft radius. Every object in that radius is destroyed, as the tree grows itself from the floor, or from a crack in the space, if there's no floor. Every creature must make a Dexterity DC save throw, or suffer 1d100 force damage and be trapped in it. With a successful save, the creature suffer half of said dice and can move freely in a square of 15ft x 15ft, with the creature in the center of it. Every end of its turn, the creature must make a new saving throw if it is still inside the tree.

As an action, the caster can choose one of the following nine effects the tree can make. It must make a 1d8 throw to know which effect will be done, unless it selects the one of the same world the tree has been summoned. Every effect can be done only once, and if the dice rolls in an used effect, it must add 1 to the value, until an unused effect is selected. Once all the effects have been used, the tree disappears, and the caster cannot summon it again for a year.
The mentioned effects are the following:

      Shine of Asgard
            Select a number of allies of the double of your spell modifier, they recover 3/4 of their hp and get 1/4 oh their total hp as an extra for a day. Also, add your spell modifier to their attack or their damage rolls (only one) until you start your next turn.

      Roar of Midgard
            Select a number of allies of the double of your spell modifier, they have three times as much actions in their turn until the start of your next turn.

      Eye of Vanaheimr
            Select a number of allies of the double of your spell modifier, they have advantage on every roll, until the tree is unsummoned or they leave a radius of 250ft of the tree.

      Army of Jötunheimr
            Select a number of allies of the double of your spell modifier. The caster must throw a 1d20, then add your spellcasting modifier. An army of that number of jotuns appear, and attack any creature that is not your selected ally. If there's no creature out of your ally range, they rest until the tree is unsummoned.

      Mist of Niflheim
            Select a number of allies of the double of your spell modifier. A mist as cold as death surrounds the tree. Every creature in a 60ft cylinder, centered in a tree must make a constitution saving throw against a 22 DC. On a failed save, the creature that's not a selected ally, will take half a 1d100 frost damage, and must make on every turn a saving throw and take again half a 1d100 frost damage. If the creature pass the saving, it only takes 1d100 frost damage once. The creature that doesn't pass the throw results immobilized until succeeding the throw.

      Wrath of Muspelheim
            The caster must place, mentally, crack spots equal to the double of their spell modifier. Each of these crack spots make one or more lines from the tree no more than 120ft away, making a line of 20ft wide of a 90ft cliff, ending in lava. If a creature is standing where the crack will pop out, it must make a 22 DC dexterity saving throw or fall directly into the pit. Every creature that falls into the pit will take 2d20 fire damage, and 1d20 force damage for every turn made, not only the creature's. Also, the crack closes at the start of the next caster's turn, if any creature is inside the pit when this happens, it takes 2d100 force damage, and has until the next start of the caster's turn to get out of the earth, or it will die.

      Wish from Helheim
            The caster must make a 1d12 throw, and choose a number of enemies equal to the throw. Every chosen enemy must make a wisdom saving throw with a DC of 22. On a failed save, the caster must choose among those who failed the save every time someone ends their turn. The chosen enemy must make another wisdom saving throw with a DC of 22. On a failed save, Jörmungandr eats them, and throws their body into Helheim.

      Aid from Nidavellir
            Select a number of allies of the double of your spell modifier. Each ally must select a weapon of its own, and for 1d12 plus the caster's spell characteristic's modifier turns they have instant critic with only hitting the target, and they have advantage on attack rolls.