  Utilising some recent ideas from our bilinear bi-parameter theory, we give an
efficient proof of a two-weight Bloom type inequality for iterated commutators
of linear bi-parameter singular integrals. We prove that if $T$ is a
bi-parameter singular integral satisfying the assumptions of the bi-parameter
representation theorem, then $$ \| [b_k,\cdots[b_2, [b_1,
T]]\cdots]\|_{L^p(\mu) \to L^p(\lambda)} \lesssim_{[\mu]_{A_p},
[\lambda]_{A_p}} \prod_{i=1}^k\|b_i\|_{\operatorname{bmo}(\nu^{\theta_i})} , $$
where $p \in (1,\infty)$, $\theta_i \in [0,1]$, $\sum_{i=1}^k\theta_i=1$, $\mu,
\lambda \in A_p$, $\nu := \mu^{1/p}\lambda^{-1/p}$. Here $A_p$ stands for the
bi-parameter weights in $\mathbb{R}^n \times \mathbb{R}^m$ and
$\operatorname{bmo}(\nu)$ is a suitable weighted little BMO space. We also
simplify the proof of the known first order case.
