Tree saplings purchased online are curved parallel to the ground

[whitenack]

Got a few white oak saplings online a few years ago. Right out of the box, the trees were bending over gently to the point that the top is parallel to the ground. They came with bamboo stakes, so I put the bamboo back on them to try to train them to grow straight. After a year or two of that, the trees were still bent (after removing the bamboo). The next year I tied a loose piece of twine to the top of the trees and pulled it straight, then tied the twine to a stake in the ground. After a year, the tree still wants to bend. Now I have removed all the crutches and left them to fend for themselves.

Is that the right thing to do? Do I need to tie them up again and just give them more time?

The trees are about 5' tall and about 1/2" to 3/4" in diameter.

 

[TheJollyLogger]

Yes, tie them up. They are still small enough to straighten.

 

[whitenack]

Yes, tie them up. They are still small enough to straighten.

Thanks. Which way is best, tie to a bamboo pole or loosely pull upright with twine to a stake?

ETA: Also, how long should I expect it to take for the tree to stand upright on its own?