I have a tall 'Cherry Red' Oleander that I would like to grow in a tree form opposed to shrub. Is it possible to train and grow it to form a small tree?
I was thinking to airlayer the 2 tall shoots in the right side of the photo below.

Oleanders are not trees, they're large shrubs. You can start new plants with one stem but they will grow more stems and be big shrubs, never single stems trees. Someone in my neighborhood bought a whole row of oleander "trees." They look terrible because to maintain the tree form, they've had to constantly cut off hundreds of stems coming up from the ground.

Lucy, I have had this Oleander for over 15+ years and it has never put out stems from the ground. The first branching off the main stem is 16" from the ground with additional branching up.

Then just prune it up until it's a tree.

I'd be hesitant to hurry about tree forming... Heavy leaf growth causes the stems to flop.

Seems like these shrubs root easily just by in-ground layering.
And... the seeds come up readily in tilled garden soil.