  For an indifference graph $G$ we define a symmetric function of increasing
spanning forests of $G$. We prove that this symmetric function satisfies
certain linear relations, which are also satisfied by the chromatic
quasisymmetric function and unicellular LLT polynomials. As a consequence we
give a combinatorial interpretation of the coefficients of the LLT polynomial
in the elementary basis (up to a factor of a power of $(q-1)$), strengthening
the description given by Alexandersson and Sulzgruber.
