  We present deep, sub-arcsecond ($\sim$2000 AU) resolution ALMA 0.82 mm
observations of the former high-mass prestellar core candidate G11.92-0.61 MM2,
recently shown to be an $\sim$500 AU-separation protobinary. Our observations
show that G11.92-0.61 MM2, located in the G11.92-0.61 protocluster, lies on a
filamentary structure traced by 0.82 mm continuum and N$_2$H$^+$(4-3) emission.
The N$_2$H$^+$(4-3) spectra are multi-peaked, indicative of multiple velocity
components along the line of sight. To analyse the gas kinematics, we performed
pixel-by-pixel Gaussian decomposition of the N$_2$H$^+$ spectra using SCOUSEPY
and hierarchical clustering of the extracted velocity components using ACORNS.
Seventy velocity- and position-coherent clusters (called "trees") are
identified in the N$_2$H$^+$-emitting gas, with the 8 largest trees accounting
for >60% of the fitted velocity components. The primary tree, with $\sim$20% of
the fitted velocity components, displays a roughly north-south velocity
gradient along the filamentary structure traced by the 0.82 mm continuum.
Analysing a $\sim$0.17 pc-long substructure, we interpret its velocity gradient
of $\sim$10.5 km s$^{-1}$pc$^{-1}$ as tracing filamentary accretion towards MM2
and estimate a mass inflow rate of $\sim$1.8$\times10^{-4}$ to
1.2$\times10^{-3}$ M$_\odot$ yr$^{-1}$. Based on the recent detection of a
bipolar molecular outflow associated with MM2, accretion onto the protobinary
is ongoing, likely fed by the larger-scale filamentary accretion flows. If 50%
of the filamentary inflow reaches the protostars, each member of the
protobinary would attain a mass of 8 M$_\odot$ within $\sim1.6\times$10$^5$ yr,
comparable to the combined timescale of the 70 $\mu$m- and MIR-weak phases
derived for ATLASGAL-TOP100 massive clumps using chemical clocks.
