Gingivitis is a non-destructive periodontal disease that causes gum tissue inflammation(swelling). A typical sign would be bleeding when brushing. If you are bleeding when you brush, you may want to consult your dentist immediately because the gingivitis can progress into periodontitis which is an irreversible destructive periodontal disease.
Gingivitis is typically caused by insufficient oral hygiene or plaque buildup. Bacteria in plague or calculus cause infection on the gum tissue and the gum tissue get swollen. This is why gum tissue can easily bleed even for brushing. Typically, your gum should not be bleeding on brushing in a normal condition, however, some medication can also induce the gingival swelling. Generally, the dental procedure that gets involved for the treating of the gingivitis would be getting a simple professional dental cleaning. It takes some times for the gingival inflammation to disappear thus the bleeding may last up to a week post op. After the dental procedure, It is very important to keep up with good oral hygiene including dental flossing to avoid any further progress of the gingivitis into periodontitis.
Periodontitis Article: [https://www.midentalclinic.com/what-is-periodontitis]
References:
https://www.mouthhealthy.org/en/az-topics/g/gingivitis
https://en.wikipedia.org/wiki/Gingivitis