pitch pine terrible nebari.

[*tree*]

Last spring I bought three pitch pine saplings and put them into the ground, I didn't do any root work on them since the were a bit weak, but they got much stronger over the last year. But now I noticed that one of them has some terrible surface roots going up and down and stuff and it had longer straigth part of the trunk anyways so I choped it and dug it up to make something smaller out of it.
I put it in a pond basket not cutting any roots and I added some 1:1 perlite and potting soil, because I suppose that if I would put some pure pumice there or just a regular bonsai soil, it would rather root into that, but I want the tree to root near the trunk so that I can do some major root work on it next spring. So was the potting soil good to use here?

 

[Shibui]

The pines I grow don't usually volunteer new roots like say trident maples and junipers do. I suspect you'll need to force your trees to generate new roots. That may include really hard root pruning.
Pines are generally quite flexible. That includes roots so is is often possible to untangle and straighten roots, even quite thick ones but I doubt your little trees have really thick roots yet. It's a pity you've already chopped the trunk because pines recover from root work much better when there are strong growing tips above. I'd suggest letting it recover this summer and doing real root work next spring.

Not sure that trees prefer to root into potting soil. Roots grow wherever conditions are good.
Putting 2 very different soil types into a container can sometimes cause problems. Root sometimes don't cross to very different soil media. Water may run right through the new free draining soil and not penetrate into the older soil in the middle. I have had trees die of dehydration because the roots could not cross to the new soil and water did not cross to the more compact older soil. Sometimes the reverse happens. You need to water a lot to keep the new soil damp to make sure the new roots can grow but the older soil stays too wet and causes root problems near the trunk.