An approach I've used is to use https://github.com/newren/git-filter-repo https://github.com/newren/git-filter-repo (amazing, versatile tool) to put the tree in

An approach I've used is to use https://github.com/newren/git-filter-repo https://github.com/newren/git-filter-repo (amazing, versatile tool) to put the tree into a subdirectory, and namespace its tags, and then merge that into another tree with --allow-unrelated-histories. I built a tool for an employer that automated this process for the purpose of consolidating an excessive number of repositories.