oddly shaped dark oak trees grown from saplings

Invslid, modded game; that's not vanilla sky rendering.

this also happens in vanilla and as soon as it grew some leaves started decaing.

Are there any blocks (previous leaves, etc) above where the tree was planted?
Does MC-123468 or MC-237375 describe your issue?

If not, then your report does not contain enough information to fully understand or reproduce the problem.
Please include a numbered list of steps along with the Observed and Expected results by Editing the Description above as shown here:

Steps to Reproduce:
1. (list every step exactly, so someone else can reproduce the issue, and try following your list to make sure you can still reproduce the issue yourself)
2.
3.
Observed Results:
(briefly describe what actually happens, including exact message(s) shown)
Expected Results:
(briefly describe what should happen)

(add screenshots or video to help explain the issue)

This report has been temporarily closed as Awaiting Response. It will automatically reopen when you add information. Please follow the format shown and include all sections (steps, observed, expected). Reports that do not contain all of the requested information and complete steps to reproduce the issue may be closed as Incomplete. For more information please read the Bug Tracker Guidelines.

You may find this Report Creation Form helpful for any future reports you create.

 MC-237375 is simillar and this happens randomly as far as I know and sometimes i find it in dark oak forests but rarly.