1)
In Divrei ha'Yamim 1 10:12, it says that they buried them under the Alah!
1.
Radak: Eshel is a general word that includes all trees. 1 The same applies to "va'Yita Eshel" (Bereishis 21:33). In Divrei ha'Yamim, it explains that the tree was an Alah (oak).
1
Malbim: It is a type of tree.
2)
Why did they fast for seven days?
1.
Radak: This corresponds to the seven days that Nachash gave them (when he threatened Yavesh Gil'ad); at that time, they were saved via Sha'ul. This is why Anshei Yavesh Gil'ad engaged in him (to retrieve his body and bury him), for they remembered the salvation through him.
