Do not focus NvimTree upon VimEnter

lua/core/autocommands.lua

@@ -22,7 +22,15 @@ local function term_close()
 end
 
 local function open_file_tree()
-    require("nvim-tree.api").tree.open()
+    local ok, mod = pcall(require, "nvim-tree.api")
+    if ok then
+        -- get current window id
+        local win = vim.api.nvim_get_current_win()
+        -- open NvimTree
+        mod.tree.open()
+        -- switch back focus to previous window
+        vim.api.nvim_set_current_win(win)
+    end
 end
 
 vim.api.nvim_create_autocmd("TermClose", {