In Creativerse, Elderwood trees can be grown from Saplings.
Other than that, two more tree Saplings exist: Ashenwood Saplings and Cragwood Saplings.
To obtain Elderwood Saplings, just harvest ("pull") blocks of Elderwood Leaves and Wood blocks from trees, no matter if these trees are small and bush-like or majestic like in some Forests.
Eventually Saplings will be added now and then.
Elderwood Saplings will even appear now and then if you place blocks of Elderwood Leaves on the ground and then pick them up again. It can take quite long though, since the additional harvest will happen completely randomly.
However, Excavators of any kind will not yield any Saplings when used on Elderwood Leaves and/or Wood. Also, harvesting Corrupted Elderwood and Corrupted Elderwood Leaves will not lead to finding any Saplings, even though they can be purified into Elderwood and Elderwood Leaves.
To make trees successfully grow, Elderwood Saplings should be planted/placed on (green) Grass, Dirt or Snow Cap. According to Playful, Saplings require moisture too, but tests did not confirm this. If you want to be on the safe side, simply place 1 block of Water or Mineral Water nearby.
However you can only grow trees on the surface with enough free space above and - most importantly - in a Biome that supports growing Elderwood trees, preferably Woodlands, Forests or Tundras.
Elderwood Saplings won't grow on most other kinds of soil, like Mud, Detritus, Matted Needles, Canyon Floor, Rocky Dirt, Dead Grass, Savannah Grass, Sand, Sandstone, tree Leaves or Mold - if you try to plant Saplings on these types of ground, a message window will appear, telling you: "Item cannot grow on this block type."
Simply take a look at the Elderwood Sapling right after placing it. If it stays "fallow" (written in red letters) even after placing water nearby, you can just tear it out again; since no trees will grow at this spot.
You can plant 2x2 Saplings or even more of them together. Then a tree with a larger stem (4 blocks thick) might grow. Or maybe two trees on top of each other. The maximum size of player-grown Elderwood trees seems to be 4x2 blocks in width, but maybe you'll be able to grow even larger trees?
You can use fertilizer (Pigsy Droppings) on Elderwood Saplings to make trees grow 15 minutes faster (but you cannot fertilize "fallow" Saplings, since they won't grow no matter what). After that you'll just have to wait.
Trees you grow yourself usually will be of small height with a symmetrical shape. They might often not have any Flowers nor Beehives on them right away, however those can grow/spawn by themselves on any tree-top later on. Player-grown Elderwood trees will not feature Rimecones on or under them, but these can be created by using a Plow on Elderwood Leaves.
If you plant Elderwood Saplings into cold biomes, their leaves might turn into Snowy Elderwood Leaves automatically.
It will take 15-16 RL-hours until trees eventually "sprout" from Saplings - unless they are "fallow" of course. It does not matter if you are online or nearby. Saplings will turn into full-grown trees instantly which you can observe if you're close at that moment.
It is possible to make Elderwood trees grow on other trees. It does not regularly happen unintended when planting Elderwood Saplings very close to each other, instead this happens a lot more easily with patches of Ashenwood Saplings or Cragwood Saplings.
Still, even triple-trees or higher "staples" of trees can be grown deliberately by placing blocks of green Grass (or Dirt or Snow Cap) with Water (or Mineral Water) on tree-tops to plant your Elderwood Sapling there.
If you put Elderwood Saplings into Flower Pots, Wood Planters, on Wall Shelves, Hidden Temple Altars or Placemats, then the Saplings will not grow into trees there, but will merely be preserved and displayed for decoration.