I can be spelt Ole or Ol and it means Old.
Example:
“ Give me a big ole hug!”
So basically you’re saying give me a very big hug.
ol" can be used to mean "old", when used on its own, but with "big" it has a different meaning: when used in conjunction with "big" like this, "'ol", is an intensifier. You're not saying that the tree is old. It's closer in meaning to saying that the tree is "very big".