Apenas para a árvore 1.6 e acima
Você pode querer olhar para:
man tree
--du For each directory report its size as the accumulation of sizes of all its files and sub-directories (and their files, and so on). The total amount of used space is also given in the final report (like the 'du -c' command.) This option requires tree to read the entire directory tree before emitting it, see BUGS AND NOTES below. Implies -s.
Então você deve usar:
tree --du -h