Mindmup WAS cool , but they choose do switch to closed source (B1TCHM0VE) , and require a Google/NSA Account as well ( Go4ckUSlts), so even their import / export function in MindSlt2 is nonsense. Luckily .mup files are simple json ,# and tiddywiki with map plugins also export/import to/from .json ... the troubles faced might be resolved...
IMAGES
both have base64 images, but mindmup defines width & height, tiddlymap needs an single image/png tiddler , icons have a size ( which shouldn't be higher than 150), so we choose to take the largest dimension and scale it by factor 0.2 ( if images in your mindmup scale to 1400px in largest dimension, use 0.1)