Put this file in `~/.local/share/applications/`

commicrosoftteams.desktop

[Desktop Entry]
Name=Microsoft Teams
Exec=webapp-container https://teams.microsoft.com --webappUrlPatterns=https?://*.microsoft*.com/* --app-id=commicrosoftteams --name="Microsoft Teams" --icon=~/.local/share/applications/commicrosoftteams.ico --store-session-cookies --enable-media-hub-audio --user-agent-string="Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0"
Icon=~/.local/share/applications/commicrosoftteams.ico
Type=Application
StartupWMClass=commicrosoftteams
OnlyShowIn=Unity
Actions=chat;teams;meetings;files

[Desktop Action teams]
Name=Teams
Exec=webapp-container https://teams.microsoft.com/_#/conversations/?ctx=channel --webappUrlPatterns=https?://*.microsoft*.com/* --app-id=commicrosoftteams --name="Microsoft Teams" --icon=~/.local/share/applications/commicrosoftteams.ico --store-session-cookies --enable-media-hub-audio --user-agent-string="Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0"

[Desktop Action chat]
Name=Chat
Exec=webapp-container https://teams.microsoft.com/_#/conversations/newchat?ctx=chat --webappUrlPatterns=https?://*.microsoft*.com/* --app-id=commicrosoftteams --name="Microsoft Teams" --icon=~/.local/share/applications/commicrosoftteams.ico --store-session-cookies --enable-media-hub-audio --user-agent-string="Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0"

[Desktop Action meetings]
Name=Meetings
Exec=webapp-container https://teams.microsoft.com/_#/calendar --webappUrlPatterns=https?://*.microsoft*.com/* --app-id=commicrosoftteams --name="Microsoft Teams" --icon=~/.local/share/applications/commicrosoftteams.ico --store-session-cookies --enable-media-hub-audio --user-agent-string="Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0"

[Desktop Action files]
Name=Files
Exec=webapp-container https://teams.microsoft.com/_#/my/file-recent --webappUrlPatterns=https?://*.microsoft*.com/* --app-id=commicrosoftteams --name="Microsoft Teams" --icon=~/.local/share/applications/commicrosoftteams.ico --store-session-cookies --enable-media-hub-audio --user-agent-string="Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Firefox/50.0"