Large Oak Trees replace blocks

1. Oak trees can grow big even with blocks above them. 
2. When tree's grown it replaces blocks with tree trunk and branches. Even bedrock
3. Easiest way to reproduce - use ilmango's "Fast 4 Type Tree Farm (Acacia, Spruce, Birch, Oak)" with oak saplings
4. Not sure if i'm allowed to leave a link, ask me if needed

Thanks!