1. Visit the website and sign up. (they have a free plan)
2. Create your Mind Map.
3. Click 'Share' menu from the bottom -> Click 'Publishing settings' option.
4. Click 'Embed map...'
5. Copy Embed code. (don't paste this into Notion. it won't work yet.)
6. Generate Notion Embedable URL
with your HTML.
7. Paste the URL into your Notion Embed block.