Elder trees are said to house Elder Women or Elder Mothers in Scandinavia and the UK.
Elder women can be loving, healing and giving, or downright deadly. They are happy to share their flowers and berries with humans as long as they ask nicely (extra points for giving her offerings like beer) and will even take away diseases and pain.
However, if you chop off her tree's branches or cut it down to make furniture or housing, she will take revenge. If you're lucky you will just wake up in the middle of the night finding an old woman sucking at your skin to get something back from you every night until you get rid of the elder tree furniture. If you're unlucky you will get sick and die.
It is also said that if you plant an elder tree in your garden, it will go for walks at night and look in through the windows.