I was leaning against a tree on the hill , sitting.
My query is whether or not we should treat "sitting" as present participle with adverbial meaning, or as past-continuous tense.
To clarify , I want to show them in example
I was leaning against a tree on the hill while sitting.
or
I was leaning against a tree on the hill and I was sitting.
What meaning does "sitting" in the original sentence ascribe to the overall meaning of the sentence?