You can parent animation layers to create hierarchical relationships in the Animation Layer Editor. See Animation layer hierarchy for more information on parent-child layer relationships.
The selected layer becomes a child of the layer you dragged it onto.
If the parent layer already has other child layers, you can expand the parent layer and drop the new child layer into any position within the hierarchy. If you drop the new child layer onto a collapsed parent, it is placed last among the child layers in the hierarchy.
To unparent an animation layer