All LGBT+ people can proudly display the rainbow flag, and that includes bisexual individuals as well as gay men, lesbians, transgender people, and anyone else who identifies as LGBT+. The rainbow flag is a symbol of solidarity for everyone who identifies as being part of the LGBT+ community. It isn't even unheard of to see straight allies wearing the rainbow flag to show support for the LGBT+ family and friends.
If you want to show pride for your bisexuality, feel free to display either the rainbow flag or the bisexual pride flag. You may also wish to wear clothing or jewelry featuring either of these flags or color schemes to show your pride.