It's been 3 days of fermentation, I added beet root for colouring in the middle of fermentation. I used china globe grape (not that red), and after hours later the bubbles getting lesser
Depending on how their processed, adding beetroot to a fermenting wine must should not do anything to inhibit fermentation. Unless your beet must is full of sorbates or other preservatives, it should be fine.
If you're mostly going for color, in the future I would add them towards the end of fermentation, as active fermentation seems to scrub out some of the bright colors, although it probably won't matter much when using beets in a wine must.