One possibilities is use of pure tikz.
For starting point may serve this (no very simple) example:
\documentclass[border=3mm]{standalone}\usepackage{tikz}\usetikzlibrary{arrows.meta, positioning, shapes.multipart, }\newcommand\ppbb{path picture bounding box}\begin{document}\begin{tikzpicture}[ node distance = 5mm and 0mm, arr/.style = {-{Straight Barb[scale=0.8]}, semithick},HMPN/.style args = {#1/#2}{% rectangle split, rectangle split parts=3, rectangle split horizontal, inner ysep=1pt, outer ysep=1pt, node contents={#1\nodepart{two}\kern-1.4pt+\kern-1.4pt\nodepart{three}#2}, path picture={\draw (\ppbb.south west) -- (\ppbb.south east);}}, ]\node (a) [HMPN=3/4]; % 3 + 4\node (b) [HMPN=1/2, below left = of a.two split south]; % 1 + 2 \draw[arr] (a.south) -- (b.three north);\node (c) [below=of b] {5}; \draw[arr] (b) -- (c);\end{tikzpicture}\end{document}