I have planted 4 saplings and cleared all blocks next to the saplings. it has 13 blocks of vertical space and also I've used 15 bone meals but no luck at growing any. what am I doing wrong? PS. I am on xbox one edition
These are spruce saplings, not dark oak saplings. Spruce needs 14 blocks above the saplings (15 including saplings) to grow; even then most growth attempts will fail; large spruce can grow even up to 30 blocks tall, so only about 1 in 30 attempts will succeed with space of 15 blocks (and none with 13).
Dark Oak would fit in the space you have prepared just fine, but dark oak saplings look like this: