/**
 *  Type that allows to create a Tree with different shape and controllable level of deepness
 * */
type Length<T extends any[]> = T['length']
type Prepend<V, T extends any[]> = ((head: V, ...args: T) => void) extends ((...args: infer R) => void)
  ? R
  : any;

/* BuildTree allow to create tree with predefined level of nesting */
type BuildTree<T, N extends number = -1, I extends any[] = []> = {
  1: T
  0: (T & { children: (BuildTree<T, N, Prepend<any, I>>)[] })
}  [ Length<I> extends N ? 1 : 0]

interface User {
  name: string;
}

type GrandUser = BuildTree<User, 2>;

const grandUser: GrandUser = {
  name: 'Grand User',
  children: [{
    name: 'Son',
    children: [{
      name: 'Grandchild',
      children: [{
        name: '123',
        children: [{
          name: 'Some other name'
        }]
      }]
    }]
  }]
};

grandUser.children[0].children[0].children[0]