I have the following integral $$\int d^D l \frac{1}{p^2 (p-l)^2 l^2}$$ which I want to rexpress using feynman parameters. I can write as a first step, $$2 \int_0^1 dx \int_o^{1-x} dy \int d^D l \frac{1}{(p^2(1-x-y) + (p-l)^2x + l^2y)^3}$$ My problem is, when I expand the term in the denominator there I get $$ p^2(1-x-y) + (p-l)^2x + l^2y = l^2(x+y) - 2l \cdot p x$$ I would then proceed by writing this in the form $(l-a)^2 + b$ from which I can use standard dim reg formulae but I can't do that here because of the $x+y$ term attached to the $l^2$.
Any advice?