It is not easy to id this bird at all. The bill points to it being one of the Lark species IMO. And I lean very much towards it being a Sparrowlark.
Female Chestnut-Backed Sparrowlark to be precise.
Let us see if we can get to it:
Feint whitish color on hind neck: it would seem so.
Heavy bill: Check.
White vent: Check.
White cheek: Check.
Furthermore it lacks a distinct eyebrow and the white above the eye seems to be restricted to a upper half of a white eye ring.
I will say that it is a Female Chestnut-Backed Sparrowlark. Did you perhaps see any males in the vicinity? You would've seen her at the end of a their peak breeding season and thus normally in company of a male. Other times they are gregarious in quite a big flock.
They very rarely perch in trees though! So if it is a Female Chestnut-Backed Sparrowlark, which I am pretty sure it is, then you did well to get it sitting in a tree.
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